1 Array, Hash Table https://leetcode.com/problems/two-sum Easy 2 Hash Table, String, Sliding Window https://leetcode.com/problems/longest-substring-without-repeating-characters Medium 3 Array, Divide and Conquer, Dynamic Programming https://leetcode.com/problems/maximum-subarray Easy 4 Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack https://leetcode.com/problems/trapping-rain-water Hard 5 Linked List, Math, Recursion https://leetcode.com/problems/add-two-numbers Medium 6 Array, Two Pointers, Sorting https://leetcode.com/problems/3sum Medium 7 String, Dynamic Programming https://leetcode.com/problems/longest-palindromic-substring Medium 8 Array, Binary Search, Divide and Conquer https://leetcode.com/problems/median-of-two-sorted-arrays Hard 9 Array, Two Pointers, Greedy https://leetcode.com/problems/container-with-most-water Medium 10 Array, Dynamic Programming https://leetcode.com/problems/best-time-to-buy-and-sell-stock Easy 11 Array, Binary Search https://leetcode.com/problems/search-in-rotated-sorted-array Medium 12 Array, Depth-First Search, Breadth-First Search, Union Find, Matrix https://leetcode.com/problems/number-of-islands Medium 13 Hash Table, Linked List, Design, Doubly-Linked List https://leetcode.com/problems/lru-cache Medium 14 Array, Sorting https://leetcode.com/problems/merge-intervals Medium 15 String, Dynamic Programming, Backtracking https://leetcode.com/problems/generate-parentheses Medium 16 Array, Two Pointers, Binary Search, Bit Manipulation https://leetcode.com/problems/find-the-duplicate-number Medium 17 Array, Prefix Sum https://leetcode.com/problems/product-of-array-except-self Medium 18 String, Stack https://leetcode.com/problems/valid-parentheses Easy 19 Array, Hash Table, Prefix Sum https://leetcode.com/problems/subarray-sum-equals-k Medium 20 Array, Dynamic Programming https://leetcode.com/problems/house-robber Medium 21 Array, Binary Search, Dynamic Programming https://leetcode.com/problems/longest-increasing-subsequence Medium 22 Linked List, Recursion https://leetcode.com/problems/reverse-linked-list Easy 23 Array, Dynamic Programming https://leetcode.com/problems/maximum-product-subarray Medium 24 Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort https://leetcode.com/problems/merge-k-sorted-lists Hard 25 Linked List, Recursion https://leetcode.com/problems/merge-two-sorted-lists Easy 26 Math, Dynamic Programming, Memoization https://leetcode.com/problems/climbing-stairs Easy 27 Array, Dynamic Programming, Breadth-First Search https://leetcode.com/problems/coin-change Medium 28 Array, Dynamic Programming, Greedy https://leetcode.com/problems/jump-game Medium 29 Hash Table, String, Dynamic Programming, Trie, Memoization https://leetcode.com/problems/word-break Medium 30 Hash Table, String, Sliding Window https://leetcode.com/problems/minimum-window-substring Hard 31 Array, Binary Search https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array Medium 32 Array, Backtracking https://leetcode.com/problems/permutations Medium 33 Array, Backtracking https://leetcode.com/problems/combination-sum Medium 34 Hash Table, String, Backtracking https://leetcode.com/problems/letter-combinations-of-a-phone-number Medium 35 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/validate-binary-search-tree Medium 36 Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue https://leetcode.com/problems/sliding-window-maximum Hard 37 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree Medium 38 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/symmetric-tree Easy 39 Array, Two Pointers https://leetcode.com/problems/next-permutation Medium 40 Array, Two Pointers, Sorting https://leetcode.com/problems/sort-colors Medium 41 Linked List, Two Pointers https://leetcode.com/problems/remove-nth-node-from-end-of-list Medium 42 Array, Bit Manipulation https://leetcode.com/problems/single-number Easy 43 Array, Stack, Monotonic Stack https://leetcode.com/problems/largest-rectangle-in-histogram Hard 44 Array, Hash Table https://leetcode.com/problems/first-missing-positive Hard 45 Depth-First Search, Breadth-First Search, Graph, Topological Sort https://leetcode.com/problems/course-schedule Medium 46 Dynamic Programming, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-maximum-path-sum Hard 47 Array, Backtracking, Matrix https://leetcode.com/problems/word-search Medium 48 Array, Backtracking, Bit Manipulation https://leetcode.com/problems/subsets Medium 49 Array, Hash Table, Union Find https://leetcode.com/problems/longest-consecutive-sequence Medium 50 Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect https://leetcode.com/problems/kth-largest-element-in-an-array Medium 51 Hash Table, String, Sorting https://leetcode.com/problems/group-anagrams Medium 52 Array, Two Pointers https://leetcode.com/problems/move-zeroes Easy 53 Hash Table, Linked List, Two Pointers https://leetcode.com/problems/intersection-of-two-linked-lists Easy 54 Array, Hash Table, Divide and Conquer, Sorting, Counting https://leetcode.com/problems/majority-element Easy 55 Math, Dynamic Programming, Combinatorics https://leetcode.com/problems/unique-paths Medium 56 Array, Math, Matrix https://leetcode.com/problems/rotate-image Medium 57 Linked List, Two Pointers, Stack, Recursion https://leetcode.com/problems/palindrome-linked-list Easy 58 String, Dynamic Programming https://leetcode.com/problems/edit-distance Hard 59 String, Dynamic Programming, Recursion https://leetcode.com/problems/regular-expression-matching Hard 60 Array, Hash Table, Divide and Conquer, Tree, Binary Tree https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal Medium 61 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/invert-binary-tree Easy 62 Array, Math, Two Pointers https://leetcode.com/problems/rotate-array Medium 63 String, Stack, Recursion https://leetcode.com/problems/decode-string Medium 64 Stack, Design https://leetcode.com/problems/min-stack Easy 65 Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect https://leetcode.com/problems/top-k-frequent-elements Medium 66 Hash Table, Linked List https://leetcode.com/problems/copy-list-with-random-pointer Medium 67 String, Dynamic Programming, Stack https://leetcode.com/problems/longest-valid-parentheses Hard 68 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/path-sum-iii Medium 69 Tree, Breadth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-level-order-traversal Medium 70 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/diameter-of-binary-tree Easy 71 Array, Dynamic Programming, Greedy https://leetcode.com/problems/jump-game-ii Medium 72 Array, Dynamic Programming https://leetcode.com/problems/partition-equal-subset-sum Medium 73 Stack, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-inorder-traversal Easy 74 Hash Table, String, Breadth-First Search https://leetcode.com/problems/word-ladder Hard 75 Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree https://leetcode.com/problems/unique-binary-search-trees Medium 76 Hash Table, Linked List, Two Pointers https://leetcode.com/problems/linked-list-cycle Easy 77 Array, Dynamic Programming, Matrix https://leetcode.com/problems/maximal-square Medium 78 String https://leetcode.com/problems/longest-common-prefix Easy 79 Array, Dynamic Programming, Greedy https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii Medium 80 Array, Dynamic Programming, Matrix https://leetcode.com/problems/minimum-path-sum Medium 81 Array, Binary Search, Divide and Conquer, Matrix https://leetcode.com/problems/search-a-2d-matrix-ii Medium 82 Math https://leetcode.com/problems/reverse-integer Medium 83 Array, Binary Search https://leetcode.com/problems/search-insert-position Easy 84 Linked List, Stack, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/flatten-binary-tree-to-linked-list Medium 85 Hash Table, String, Design, Trie https://leetcode.com/problems/implement-trie-prefix-tree Medium 86 Array, Stack, Monotonic Stack https://leetcode.com/problems/daily-temperatures Medium 87 Hash Table, Two Pointers, String, Greedy https://leetcode.com/problems/partition-labels Medium 88 Math, Dynamic Programming, Breadth-First Search https://leetcode.com/problems/perfect-squares Medium 89 String, Dynamic Programming https://leetcode.com/problems/decode-ways Medium 90 Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream https://leetcode.com/problems/find-median-from-data-stream Hard 91 Array, Dynamic Programming, Stack, Matrix, Monotonic Stack https://leetcode.com/problems/maximal-rectangle Hard 92 Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting https://leetcode.com/problems/task-scheduler Medium 93 Linked List, Recursion https://leetcode.com/problems/reverse-nodes-in-k-group Hard 94 Array, Matrix, Simulation https://leetcode.com/problems/spiral-matrix Medium 95 Array, Dynamic Programming, Backtracking https://leetcode.com/problems/target-sum Medium 96 Array, Hash Table https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array Easy 97 Depth-First Search, Breadth-First Search, Graph, Topological Sort https://leetcode.com/problems/course-schedule-ii Medium 98 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/merge-two-binary-trees Easy 99 String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree https://leetcode.com/problems/serialize-and-deserialize-binary-tree Hard 100 Hash Table, Linked List, Two Pointers https://leetcode.com/problems/linked-list-cycle-ii Medium 101 Dynamic Programming, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/house-robber-iii Medium 102 Linked List, Two Pointers, Divide and Conquer, Sorting, Merge Sort https://leetcode.com/problems/sort-list Medium 103 Hash Table, String, Sliding Window https://leetcode.com/problems/find-all-anagrams-in-a-string Medium 104 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-right-side-view Medium 105 String, Dynamic Programming https://leetcode.com/problems/palindromic-substrings Medium 106 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/maximum-depth-of-binary-tree Easy 107 Array, Breadth-First Search, Matrix https://leetcode.com/problems/rotting-oranges Medium 108 Array, Hash Table, Matrix https://leetcode.com/problems/set-matrix-zeroes Medium 109 Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree Easy 110 Array, Binary Search, Matrix https://leetcode.com/problems/search-a-2d-matrix Medium 111 Array, Binary Search https://leetcode.com/problems/find-minimum-in-rotated-sorted-array Medium 112 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/populating-next-right-pointers-in-each-node Medium 113 Array, Two Pointers https://leetcode.com/problems/remove-duplicates-from-sorted-array Easy 114 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/kth-smallest-element-in-a-bst Medium 115 Array, Binary Search, Sliding Window, Prefix Sum https://leetcode.com/problems/minimum-size-subarray-sum Medium 116 Array, Hash Table https://leetcode.com/problems/find-all-duplicates-in-an-array Medium 117 Array, Dynamic Programming https://leetcode.com/problems/burst-balloons Hard 118 Dynamic Programming, Bit Manipulation https://leetcode.com/problems/counting-bits Easy 119 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/all-nodes-distance-k-in-binary-tree Medium 120 Linked List, Recursion https://leetcode.com/problems/swap-nodes-in-pairs Medium 121 Linked List https://leetcode.com/problems/reverse-linked-list-ii Medium 122 Array, String, Backtracking, Trie, Matrix https://leetcode.com/problems/word-search-ii Hard 123 String, Dynamic Programming https://leetcode.com/problems/longest-common-subsequence Medium 124 Array, Binary Search, Sorting, Heap (Priority Queue), Matrix https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix Medium 125 Array, Two Pointers, Sorting https://leetcode.com/problems/4sum Medium 126 Array, Dynamic Programming https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii Hard 127 Array, Dynamic Programming https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown Medium 128 String, Dynamic Programming, Backtracking https://leetcode.com/problems/palindrome-partitioning Medium 129 Linked List, Two Pointers, Stack, Recursion https://leetcode.com/problems/reorder-list Medium 130 Array, Dynamic Programming https://leetcode.com/problems/min-cost-climbing-stairs Easy 131 Array, Depth-First Search, Breadth-First Search, Union Find, Matrix https://leetcode.com/problems/max-area-of-island Medium 132 Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set https://leetcode.com/problems/count-of-smaller-numbers-after-self Hard 133 Array, Two Pointers, Sorting https://leetcode.com/problems/3sum-closest Medium 134 Tree, Breadth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal Medium 135 Array, Binary Search https://leetcode.com/problems/find-peak-element Medium 136 Array, Hash Table, Math, Design, Randomized https://leetcode.com/problems/insert-delete-getrandom-o1 Medium 137 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/balanced-binary-tree Easy 138 Math https://leetcode.com/problems/palindrome-number Easy 139 Array, Backtracking https://leetcode.com/problems/n-queens Hard 140 Array, Math, Divide and Conquer, Geometry, Sorting, Heap (Priority Queue), Quickselect https://leetcode.com/problems/k-closest-points-to-origin Medium 141 Linked List https://leetcode.com/problems/odd-even-linked-list Medium 142 Depth-First Search, Breadth-First Search, Graph, Topological Sort https://leetcode.com/problems/minimum-height-trees Medium 143 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/same-tree Easy 144 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree Easy 145 Array, Two Pointers, Stack, Greedy, Sorting, Monotonic Stack https://leetcode.com/problems/shortest-unsorted-continuous-subarray Medium 146 Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator https://leetcode.com/problems/binary-search-tree-iterator Medium 147 Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization https://leetcode.com/problems/longest-increasing-path-in-a-matrix Hard 148 Array, Greedy, Sorting https://leetcode.com/problems/queue-reconstruction-by-height Medium 149 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/path-sum Easy 150 Tree, Binary Search Tree, Binary Tree https://leetcode.com/problems/delete-node-in-a-bst Medium 151 Tree, Depth-First Search, String Matching, Binary Tree, Hash Function https://leetcode.com/problems/subtree-of-another-tree Easy 152 Array, Hash Table, Math, Bit Manipulation, Sorting https://leetcode.com/problems/missing-number Easy 153 String, Dynamic Programming https://leetcode.com/problems/longest-palindromic-subsequence Medium 154 Array, Depth-First Search, Breadth-First Search, Union Find, Graph, Shortest Path https://leetcode.com/problems/evaluate-division Medium 155 Array, Dynamic Programming https://leetcode.com/problems/house-robber-ii Medium 156 Array, Dynamic Programming https://leetcode.com/problems/pascals-triangle Easy 157 Hash Table, Depth-First Search, Breadth-First Search, Graph https://leetcode.com/problems/clone-graph Medium 158 Array, Dynamic Programming https://leetcode.com/problems/coin-change-2 Medium 159 Hash Table, Math, Two Pointers https://leetcode.com/problems/happy-number Easy 160 Depth-First Search, Breadth-First Search, Union Find, Graph https://leetcode.com/problems/number-of-provinces Medium 161 Array, Binary Search https://leetcode.com/problems/single-element-in-a-sorted-array Medium 162 Array, Greedy https://leetcode.com/problems/gas-station Medium 163 Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree https://leetcode.com/problems/unique-binary-search-trees-ii Medium 164 Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Heap (Priority Queue), Shortest Path https://leetcode.com/problems/cheapest-flights-within-k-stops Medium 165 Linked List, Two Pointers https://leetcode.com/problems/middle-of-the-linked-list Easy 166 String, Stack, Greedy, Monotonic Stack https://leetcode.com/problems/remove-k-digits Medium 167 Array, Backtracking, Matrix https://leetcode.com/problems/sudoku-solver Hard 168 Array, Depth-First Search, Breadth-First Search, Union Find, Matrix https://leetcode.com/problems/surrounded-regions Medium 169 Binary Search, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/count-complete-tree-nodes Medium 170 String, Backtracking, Breadth-First Search https://leetcode.com/problems/remove-invalid-parentheses Hard 171 Array, Dynamic Programming, Backtracking, Bit Manipulation, Memoization, Bitmask https://leetcode.com/problems/partition-to-k-equal-sum-subsets Medium 172 Array, Two Pointers, Binary Search https://leetcode.com/problems/two-sum-ii-input-array-is-sorted Easy 173 Hash Table, String, Queue, Counting https://leetcode.com/problems/first-unique-character-in-a-string Easy 174 String, Greedy, Sorting https://leetcode.com/problems/largest-number Medium 175 Array, Math, Enumeration, Number Theory https://leetcode.com/problems/count-primes Medium 176 Array, Two Pointers, Sorting https://leetcode.com/problems/squares-of-a-sorted-array Easy 177 Array, Backtracking https://leetcode.com/problems/permutations-ii Medium 178 Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization https://leetcode.com/problems/word-break-ii Hard 179 Array, Backtracking https://leetcode.com/problems/combination-sum-ii Medium 180 Array, Dynamic Programming https://leetcode.com/problems/triangle Medium 181 Linked List, Recursion https://leetcode.com/problems/remove-linked-list-elements Easy 182 Linked List, Two Pointers https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii Medium 183 Array, Hash Table, Matrix https://leetcode.com/problems/valid-sudoku Medium 184 Backtracking, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/path-sum-ii Medium 185 Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree Medium 186 Array https://leetcode.com/problems/insert-interval Medium 187 String, Dynamic Programming, Greedy, Recursion https://leetcode.com/problems/wildcard-matching Hard 188 Array, Backtracking, Bit Manipulation https://leetcode.com/problems/subsets-ii Medium 189 Array, Dynamic Programming, Matrix https://leetcode.com/problems/unique-paths-ii Medium 190 Array, Binary Search, Dynamic Programming, Greedy https://leetcode.com/problems/split-array-largest-sum Hard 191 Hash Table, String, Greedy, Sorting, Heap (Priority Queue), Counting https://leetcode.com/problems/reorganize-string Medium 192 Hash Table, Two Pointers, String, Sliding Window https://leetcode.com/problems/permutation-in-string Medium 193 Array, Hash Table, Sorting, Counting https://leetcode.com/problems/majority-element-ii Medium 194 Array, Hash Table, Divide and Conquer, Tree, Binary Tree https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal Medium 195 Array, Dynamic Programming https://leetcode.com/problems/minimum-cost-for-tickets Medium 196 Hash Table, String, Trie, Sorting, Heap (Priority Queue), Bucket Sort, Counting https://leetcode.com/problems/top-k-frequent-words Medium 197 Array, Depth-First Search, Breadth-First Search, Matrix https://leetcode.com/problems/island-perimeter Easy 198 Linked List https://leetcode.com/problems/remove-duplicates-from-sorted-list Easy 199 Math, String, Bit Manipulation, Simulation https://leetcode.com/problems/add-binary Easy 200 Array, Dynamic Programming, Breadth-First Search, Matrix https://leetcode.com/problems/01-matrix Medium 201 Hash Table, String, Sorting https://leetcode.com/problems/valid-anagram Easy 202 Math, String, Simulation https://leetcode.com/problems/multiply-strings Medium 203 Binary Search, Interactive https://leetcode.com/problems/first-bad-version Easy 204 String, Depth-First Search, Design, Trie https://leetcode.com/problems/design-add-and-search-words-data-structure Medium 205 Array, Stack, Monotonic Stack https://leetcode.com/problems/next-greater-element-ii Medium 206 Math, String, Stack https://leetcode.com/problems/basic-calculator-ii Medium 207 Array, String, Depth-First Search, Breadth-First Search, Union Find https://leetcode.com/problems/accounts-merge Medium 208 Two Pointers, String, Greedy https://leetcode.com/problems/valid-palindrome-ii Easy 209 Linked List https://leetcode.com/problems/delete-node-in-a-linked-list Easy 210 Array, Two Pointers https://leetcode.com/problems/interval-list-intersections Medium 211 Linked List, Two Pointers https://leetcode.com/problems/rotate-list Medium 212 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/sum-root-to-leaf-numbers Medium 213 Array, Dynamic Programming, Matrix https://leetcode.com/problems/dungeon-game Hard 214 Math, Recursion https://leetcode.com/problems/powx-n Medium 215 Array, Binary Search, Sliding Window, Prefix Sum https://leetcode.com/problems/max-consecutive-ones-iii Medium 216 Array, Hash Table, Two Pointers, Binary Search, Sorting https://leetcode.com/problems/intersection-of-two-arrays-ii Easy 217 String, Stack, Greedy, Monotonic Stack https://leetcode.com/problems/remove-duplicate-letters Medium 218 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/recover-binary-search-tree Medium 219 Depth-First Search, Breadth-First Search, Union Find, Graph https://leetcode.com/problems/is-graph-bipartite Medium 220 Array, Hash Table, Prefix Sum https://leetcode.com/problems/contiguous-array Medium 221 Array, Two Pointers, Binary Search, Sorting, Heap (Priority Queue) https://leetcode.com/problems/find-k-closest-elements Medium 222 Two Pointers, String, Recursion https://leetcode.com/problems/reverse-string Easy 223 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/range-sum-of-bst Easy 224 Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting https://leetcode.com/problems/sort-characters-by-frequency Medium 225 Hash Table, String, Sliding Window https://leetcode.com/problems/longest-repeating-character-replacement Medium 226 Stack, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-postorder-traversal Easy 227 Array, Bit Manipulation https://leetcode.com/problems/single-number-ii Medium 228 Hash Table, Math, Dynamic Programming, Heap (Priority Queue) https://leetcode.com/problems/ugly-number-ii Medium 229 Depth-First Search, Graph, Eulerian Circuit https://leetcode.com/problems/reconstruct-itinerary Hard 230 Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set https://leetcode.com/problems/the-skyline-problem Hard 231 Array, Bit Manipulation https://leetcode.com/problems/single-number-iii Medium 232 Two Pointers, String, Dynamic Programming https://leetcode.com/problems/is-subsequence Easy 233 Depth-First Search, Breadth-First Search, Graph, Heap (Priority Queue), Shortest Path https://leetcode.com/problems/network-delay-time Medium 234 String, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-paths Easy 235 Hash Table, String, Divide and Conquer, Sliding Window https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters Medium 236 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/minimum-depth-of-binary-tree Easy 237 Array, Dynamic Programming, Greedy https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee Medium 238 Array https://leetcode.com/problems/non-decreasing-array Medium 239 String, Dynamic Programming https://leetcode.com/problems/interleaving-string Medium 240 Array, Matrix, Simulation https://leetcode.com/problems/game-of-life Medium 241 Array, Backtracking https://leetcode.com/problems/combinations Medium 242 Stack, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-preorder-traversal Easy 243 Backtracking, Depth-First Search, Breadth-First Search, Graph https://leetcode.com/problems/all-paths-from-source-to-target Medium 244 Array, Math https://leetcode.com/problems/plus-one Easy 245 Array, Dynamic Programming https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv Hard 246 Array, Greedy https://leetcode.com/problems/increasing-triplet-subsequence Medium 247 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/trim-a-binary-search-tree Medium 248 Two Pointers, String, Stack, Simulation https://leetcode.com/problems/backspace-string-compare Easy 249 Array, Binary Search, Dynamic Programming, Sliding Window, Rolling Hash, Hash Function https://leetcode.com/problems/maximum-length-of-repeated-subarray Medium 250 Array, Binary Search, Greedy https://leetcode.com/problems/capacity-to-ship-packages-within-d-days Medium 251 Two Pointers, String, String Matching https://leetcode.com/problems/implement-strstr Easy 252 Hash Table, String, Backtracking, Breadth-First Search https://leetcode.com/problems/word-ladder-ii Hard 253 Array, Sliding Window https://leetcode.com/problems/subarray-product-less-than-k Medium 254 Array, Hash Table, Sorting https://leetcode.com/problems/contains-duplicate Easy 255 Linked List, Depth-First Search, Doubly-Linked List https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list Medium 256 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii Medium 257 Array, Divide and Conquer, Stack, Tree, Monotonic Stack, Binary Tree https://leetcode.com/problems/maximum-binary-tree Medium 258 String, Stack https://leetcode.com/problems/minimum-remove-to-make-valid-parentheses Medium 259 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/distribute-coins-in-binary-tree Medium 260 Depth-First Search, Graph, Biconnected Component https://leetcode.com/problems/critical-connections-in-a-network Hard 261 Math, String, Stack, Recursion https://leetcode.com/problems/basic-calculator Hard 262 Depth-First Search, Breadth-First Search, Union Find, Graph https://leetcode.com/problems/redundant-connection Medium 263 Hash Table, String https://leetcode.com/problems/jewels-and-stones Easy 264 Array, Dynamic Programming, Greedy, Sorting https://leetcode.com/problems/non-overlapping-intervals Medium 265 Array, Depth-First Search, Breadth-First Search, Matrix https://leetcode.com/problems/flood-fill Easy 266 String https://leetcode.com/problems/zigzag-conversion Medium 267 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/maximum-width-of-binary-tree Medium 268 Math, Recursion https://leetcode.com/problems/permutation-sequence Hard 269 Array, Stack, Tree, Binary Search Tree, Monotonic Stack, Binary Tree https://leetcode.com/problems/construct-binary-search-tree-from-preorder-traversal Medium 270 Math, String, Dynamic Programming, Recursion, Memoization https://leetcode.com/problems/different-ways-to-add-parentheses Medium 271 Array, Binary Search https://leetcode.com/problems/search-in-rotated-sorted-array-ii Medium 272 Linked List, Math, Stack https://leetcode.com/problems/add-two-numbers-ii Medium 273 Hash Table, Two Pointers, Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/two-sum-iv-input-is-a-bst Easy 274 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/convert-bst-to-greater-tree Medium 275 Linked List, Two Pointers https://leetcode.com/problems/partition-list Medium 276 Math, Binary Search https://leetcode.com/problems/sqrtx Easy 277 Hash Table, String https://leetcode.com/problems/isomorphic-strings Easy 278 Array, Dynamic Programming, Binary Indexed Tree, Segment Tree https://leetcode.com/problems/number-of-longest-increasing-subsequence Medium 279 Array, Binary Search https://leetcode.com/problems/binary-search Easy 280 String, Dynamic Programming, Stack, Greedy https://leetcode.com/problems/valid-parenthesis-string Medium 281 String, String Matching https://leetcode.com/problems/repeated-substring-pattern Easy 282 Array, Two Pointers https://leetcode.com/problems/remove-element Easy 283 Array, Dynamic Programming https://leetcode.com/problems/combination-sum-iv Medium 284 String, Dynamic Programming https://leetcode.com/problems/distinct-subsequences Hard 285 Array, Stack https://leetcode.com/problems/asteroid-collision Medium 286 Array, Math, Dynamic Programming, Sorting https://leetcode.com/problems/largest-divisible-subset Medium 287 Array, Depth-First Search, Breadth-First Search, Matrix https://leetcode.com/problems/pacific-atlantic-water-flow Medium 288 Array, Binary Search, Stack, Monotonic Stack, Ordered Set https://leetcode.com/problems/132-pattern Medium 289 Array, Hash Table, Dynamic Programming https://leetcode.com/problems/delete-and-earn Medium 290 Array, Dynamic Programming, Stack, Monotonic Stack https://leetcode.com/problems/sum-of-subarray-minimums Medium 291 Array, Dynamic Programming, Matrix https://leetcode.com/problems/count-square-submatrices-with-all-ones Medium 292 String, Dynamic Programming https://leetcode.com/problems/palindrome-partitioning-ii Hard 293 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/sum-of-left-leaves Easy 294 Bit Manipulation https://leetcode.com/problems/hamming-distance Easy 295 Stack, Tree, Depth-First Search, Design, Queue, Iterator https://leetcode.com/problems/flatten-nested-list-iterator Medium 296 String, Stack https://leetcode.com/problems/score-of-parentheses Medium 297 Array, Hash Table, Two Pointers, String, Dynamic Programming https://leetcode.com/problems/longest-string-chain Medium 298 Two Pointers, String https://leetcode.com/problems/valid-palindrome Easy 299 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/longest-univalue-path Medium 300 String, Backtracking, Bit Manipulation https://leetcode.com/problems/letter-case-permutation Medium 301 Tree, Breadth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-level-order-traversal-ii Medium 302 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/find-duplicate-subtrees Medium 303 Dynamic Programming, Stack, Greedy, Monotonic Stack https://leetcode.com/problems/minimum-cost-tree-from-leaf-values Medium 304 Hash Table, Linked List, Design, Doubly-Linked List https://leetcode.com/problems/lfu-cache Hard 305 Array, Binary Search, Dynamic Programming, Sorting https://leetcode.com/problems/russian-doll-envelopes Hard 306 Array, Binary Search, Dynamic Programming, Sorting https://leetcode.com/problems/maximum-profit-in-job-scheduling Hard 307 Math, String, Simulation https://leetcode.com/problems/add-strings Easy 308 Array, Hash Table, Counting https://leetcode.com/problems/pairs-of-songs-with-total-durations-divisible-by-60 Medium 309 Stack, Design, Queue https://leetcode.com/problems/implement-queue-using-stacks Easy 310 Array, Hash Table, Bit Manipulation, Trie https://leetcode.com/problems/maximum-xor-of-two-numbers-in-an-array Medium 311 Hash Table, Math, String https://leetcode.com/problems/roman-to-integer Easy 312 Array, Hash Table, Graph https://leetcode.com/problems/find-the-town-judge Easy 313 Array, Heap (Priority Queue) https://leetcode.com/problems/find-k-pairs-with-smallest-sums Medium 314 Array, Two Pointers, Sorting https://leetcode.com/problems/merge-sorted-array Easy 315 String, Stack https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string Easy 316 Two Pointers, String https://leetcode.com/problems/reverse-words-in-a-string Medium 317 Array, Hash Table https://leetcode.com/problems/4sum-ii Medium 318 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/average-of-levels-in-binary-tree Easy 319 Array, Prefix Sum https://leetcode.com/problems/find-pivot-index Easy 320 Array, Hash Table, Sorting, Counting https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number Easy 321 Hash Table, Math, String https://leetcode.com/problems/integer-to-roman Medium 322 Depth-First Search, Breadth-First Search, Graph https://leetcode.com/problems/keys-and-rooms Medium 323 Math, Bit Manipulation, Recursion https://leetcode.com/problems/power-of-two Easy 324 Array, Hash Table, Sliding Window, Counting https://leetcode.com/problems/subarrays-with-k-different-integers Hard 325 Array, Math, Dynamic Programming, Recursion, Game Theory https://leetcode.com/problems/predict-the-winner Medium 326 Array, Divide and Conquer, Dynamic Programming, Queue, Monotonic Queue https://leetcode.com/problems/maximum-sum-circular-subarray Medium 327 Math, Dynamic Programming, Recursion, Memoization https://leetcode.com/problems/fibonacci-number Easy 328 Divide and Conquer, Bit Manipulation https://leetcode.com/problems/reverse-bits Easy 329 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/delete-nodes-and-return-forest Medium 330 Array, Binary Search, Queue, Sliding Window, Heap (Priority Queue), Prefix Sum, Monotonic Queue https://leetcode.com/problems/shortest-subarray-with-sum-at-least-k Hard 331 Array, Binary Search https://leetcode.com/problems/find-minimum-in-rotated-sorted-array-ii Hard 332 Hash Table, String https://leetcode.com/problems/word-pattern Easy 333 Array, Dynamic Programming https://leetcode.com/problems/arithmetic-slices Medium 334 Array, String, Dynamic Programming https://leetcode.com/problems/ones-and-zeroes Medium 335 Array, Backtracking, Bit Manipulation, Matrix https://leetcode.com/problems/unique-paths-iii Hard 336 Array, Design, Binary Indexed Tree, Segment Tree https://leetcode.com/problems/range-sum-query-mutable Medium 337 Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/vertical-order-traversal-of-a-binary-tree Hard 338 Array, Greedy https://leetcode.com/problems/candy Hard 339 Array, Two Pointers https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii Medium 340 Hash Table, String, Trie, Sorting https://leetcode.com/problems/number-of-matching-subsequences Medium 341 Array, Binary Search https://leetcode.com/problems/koko-eating-bananas Medium 342 Array, Hash Table, String, Breadth-First Search https://leetcode.com/problems/open-the-lock Medium 343 String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Search Tree, Binary Tree https://leetcode.com/problems/serialize-and-deserialize-bst Medium 344 Array, Backtracking https://leetcode.com/problems/combination-sum-iii Medium 345 Array, Hash Table, String, Trie https://leetcode.com/problems/palindrome-pairs Hard 346 Array, Hash Table, String https://leetcode.com/problems/verifying-an-alien-dictionary Easy 347 Array, Math, Stack https://leetcode.com/problems/evaluate-reverse-polish-notation Medium 348 Array, Breadth-First Search, Heap (Priority Queue), Matrix https://leetcode.com/problems/trapping-rain-water-ii Hard 349 Array, Sliding Window, Prefix Sum https://leetcode.com/problems/maximum-points-you-can-obtain-from-cards Medium 350 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/cousins-in-binary-tree Easy 351 Math, Bit Manipulation https://leetcode.com/problems/divide-two-integers Medium 352 String, Dynamic Programming https://leetcode.com/problems/delete-operation-for-two-strings Medium 353 Array, Greedy, Sorting https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons Medium 354 Array, Hash Table, Prefix Sum https://leetcode.com/problems/subarray-sums-divisible-by-k Medium 355 Two Pointers, String https://leetcode.com/problems/count-binary-substrings Easy 356 String, Backtracking https://leetcode.com/problems/restore-ip-addresses Medium 357 Array, Matrix, Simulation https://leetcode.com/problems/spiral-matrix-ii Medium 358 Hash Table, Stack, Design, Ordered Set https://leetcode.com/problems/maximum-frequency-stack Hard 359 Math, Dynamic Programming https://leetcode.com/problems/integer-break Medium 360 Array, Two Pointers, Sorting https://leetcode.com/problems/sort-array-by-parity Easy 361 Dynamic Programming, Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-cameras Hard 362 Array, Dynamic Programming, Greedy https://leetcode.com/problems/wiggle-subsequence Medium 363 Array, Depth-First Search, Breadth-First Search https://leetcode.com/problems/jump-game-iii Medium 364 Bit Manipulation https://leetcode.com/problems/number-of-1-bits Easy 365 Tree, Binary Search Tree, Binary Tree https://leetcode.com/problems/insert-into-a-binary-search-tree Medium 366 Array, Math, Sorting https://leetcode.com/problems/maximum-product-of-three-numbers Easy 367 Math, String, Backtracking https://leetcode.com/problems/expression-add-operators Hard 368 Math, String https://leetcode.com/problems/excel-sheet-column-title Easy 369 Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set https://leetcode.com/problems/reverse-pairs Hard 370 Dynamic Programming, Tree, Depth-First Search, Graph https://leetcode.com/problems/sum-of-distances-in-tree Hard 371 Array, Greedy, Sorting https://leetcode.com/problems/two-city-scheduling Medium 372 String, Stack https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii Medium 373 Array, Design, Matrix, Prefix Sum https://leetcode.com/problems/range-sum-query-2d-immutable Medium 374 Math, Dynamic Programming https://leetcode.com/problems/2-keys-keyboard Medium 375 Array, Hash Table, Two Pointers, Binary Search, Sorting https://leetcode.com/problems/intersection-of-two-arrays Easy 376 Array, Stack, Simulation https://leetcode.com/problems/validate-stack-sequences Medium 377 Hash Table, String, Greedy https://leetcode.com/problems/longest-palindrome Easy 378 Tree, Binary Search Tree, Binary Tree https://leetcode.com/problems/search-in-a-binary-search-tree Easy 379 Array, Dynamic Programming, Greedy, Heap (Priority Queue) https://leetcode.com/problems/minimum-number-of-refueling-stops Hard 380 Array, Two Pointers, Binary Search, Greedy, Sorting https://leetcode.com/problems/valid-triangle-number Medium 381 Dynamic Programming, Tree, Recursion, Memoization, Binary Tree https://leetcode.com/problems/all-possible-full-binary-trees Medium 382 Two Pointers, String https://leetcode.com/problems/reverse-words-in-a-string-iii Easy 383 Math, String https://leetcode.com/problems/excel-sheet-column-number Easy 384 Array, Dynamic Programming, Matrix https://leetcode.com/problems/cherry-pickup Hard 385 Array, Hash Table, Linked List, Design, Hash Function https://leetcode.com/problems/design-hashmap Easy 386 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/binary-tree-pruning Medium 387 Math, Bit Manipulation https://leetcode.com/problems/sum-of-two-integers Medium 388 Stack, Design, Monotonic Stack, Data Stream https://leetcode.com/problems/online-stock-span Medium 389 Linked List, Math https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer Easy 390 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree Medium 391 Array https://leetcode.com/problems/max-consecutive-ones Easy 392 Array, Prefix Sum https://leetcode.com/problems/running-sum-of-1d-array Easy 393 Math, Greedy https://leetcode.com/problems/maximum-swap Medium 394 String, Rolling Hash, String Matching, Hash Function https://leetcode.com/problems/shortest-palindrome Hard 395 Depth-First Search, Union Find, Graph https://leetcode.com/problems/most-stones-removed-with-same-row-or-column Medium 396 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/maximum-difference-between-node-and-ancestor Medium 397 Array, Dynamic Programming https://leetcode.com/problems/frog-jump Hard 398 Array, Dynamic Programming https://leetcode.com/problems/pascals-triangle-ii Easy 399 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/deepest-leaves-sum Medium 400 Array, Depth-First Search, Breadth-First Search, Matrix https://leetcode.com/problems/shortest-bridge Medium 401 Bit Manipulation https://leetcode.com/problems/bitwise-and-of-numbers-range Medium 402 Math, Binary Search, Dynamic Programming https://leetcode.com/problems/super-egg-drop Hard 403 Array, Sliding Window, Sorting, Bucket Sort, Ordered Set https://leetcode.com/problems/contains-duplicate-iii Medium 404 Math, String, Simulation https://leetcode.com/problems/robot-bounded-in-circle Medium 405 Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/increasing-order-search-tree Easy 406 Array, Hash Table, String https://leetcode.com/problems/find-common-characters Easy 407 Array, Two Pointers, String https://leetcode.com/problems/shortest-distance-to-a-character Easy 408 Array, Greedy https://leetcode.com/problems/can-place-flowers Easy 409 Array, Hash Table, Sliding Window https://leetcode.com/problems/contains-duplicate-ii Easy 410 Array, Hash Table, Math, Counting https://leetcode.com/problems/number-of-good-pairs Easy 411 String, Stack, Greedy https://leetcode.com/problems/minimum-add-to-make-parentheses-valid Medium 412 Array, Dynamic Programming, Greedy, Sorting https://leetcode.com/problems/maximum-length-of-pair-chain Medium 413 Depth-First Search, Breadth-First Search, Union Find, Graph https://leetcode.com/problems/possible-bipartition Medium 414 Array, Hash Table, Greedy, Heap (Priority Queue) https://leetcode.com/problems/split-array-into-consecutive-subsequences Medium 415 Array, Depth-First Search, Breadth-First Search, Union Find, Matrix https://leetcode.com/problems/making-a-large-island Hard 416 Array, Breadth-First Search, Matrix https://leetcode.com/problems/shortest-path-in-binary-matrix Medium 417 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/count-good-nodes-in-binary-tree Medium 418 Array https://leetcode.com/problems/shuffle-the-array Easy 419 Array, Hash Table, Sliding Window, Heap (Priority Queue) https://leetcode.com/problems/sliding-window-median Hard 420 Array, Binary Search https://leetcode.com/problems/kth-missing-positive-number Easy 421 Array, Binary Search https://leetcode.com/problems/peak-index-in-a-mountain-array Easy 422 Array, Linked List, Stack, Monotonic Stack https://leetcode.com/problems/next-greater-node-in-linked-list Medium 423 Array, Dynamic Programming https://leetcode.com/problems/minimum-swaps-to-make-sequences-increasing Hard 424 Array, Divide and Conquer, Sorting, Quickselect https://leetcode.com/problems/wiggle-sort-ii Medium 425 Array, Hash Table, Greedy, Sliding Window, Sorting, Heap (Priority Queue) https://leetcode.com/problems/smallest-range-covering-elements-from-k-lists Hard 426 Math, String, Recursion https://leetcode.com/problems/integer-to-english-words Hard 427 Array, Dynamic Programming https://leetcode.com/problems/partition-array-for-maximum-sum Medium 428 Array, Sorting, Bucket Sort, Radix Sort https://leetcode.com/problems/maximum-gap Hard 429 Tree, Depth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/find-mode-in-binary-search-tree Easy 430 Array, Hash Table, Binary Search, Dynamic Programming https://leetcode.com/problems/longest-arithmetic-subsequence Medium 431 Array, Dynamic Programming https://leetcode.com/problems/last-stone-weight-ii Medium 432 Array, Heap (Priority Queue) https://leetcode.com/problems/last-stone-weight Easy 433 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/find-bottom-left-tree-value Medium 434 Depth-First Search, Breadth-First Search, Union Find, Graph https://leetcode.com/problems/regions-cut-by-slashes Medium 435 Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask https://leetcode.com/problems/beautiful-arrangement Medium 436 Array, Dynamic Programming, Matrix https://leetcode.com/problems/minimum-falling-path-sum Medium 437 Array, Matrix, Simulation https://leetcode.com/problems/diagonal-traverse Medium 438 Array, Queue, Sliding Window, Heap (Priority Queue), Ordered Set, Monotonic Queue https://leetcode.com/problems/longest-continuous-subarray-with-absolute-diff-less-than-or-equal-to-limit Medium 439 Bit Manipulation https://leetcode.com/problems/number-complement Easy 440 Math, Binary Search https://leetcode.com/problems/valid-perfect-square Easy 441 Math, Binary Search https://leetcode.com/problems/arranging-coins Easy 442 Math, Two Pointers, String https://leetcode.com/problems/next-greater-element-iii Medium 443 Array, Binary Search, Depth-First Search, Breadth-First Search, Union Find, Heap (Priority Queue), Matrix https://leetcode.com/problems/path-with-minimum-effort Medium 444 Array, String, Trie https://leetcode.com/problems/search-suggestions-system Medium 445 Array, Two Pointers, Matrix, Simulation https://leetcode.com/problems/flipping-an-image Easy 446 Tree, Design, Binary Search Tree, Heap (Priority Queue), Binary Tree, Data Stream https://leetcode.com/problems/kth-largest-element-in-a-stream Easy 447 Array, Binary Search, Dynamic Programming, Matrix, Ordered Set https://leetcode.com/problems/max-sum-of-rectangle-no-larger-than-k Hard 448 Hash Table, String, Binary Search, Design https://leetcode.com/problems/time-based-key-value-store Medium 449 Linked List, Sorting https://leetcode.com/problems/insertion-sort-list Medium 450 Two Pointers, String https://leetcode.com/problems/string-compression Medium 451 Tree, Depth-First Search, Breadth-First Search https://leetcode.com/problems/maximum-depth-of-n-ary-tree Easy 452 Math https://leetcode.com/problems/factorial-trailing-zeroes Medium 453 Array, Sorting, Heap (Priority Queue), Simulation, Prefix Sum https://leetcode.com/problems/car-pooling Medium 454 Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/find-largest-value-in-each-tree-row Medium 455 String, Dynamic Programming https://leetcode.com/problems/shortest-common-supersequence Hard 456 Dynamic Programming https://leetcode.com/problems/number-of-dice-rolls-with-target-sum Medium 457 Hash Table, Linked List, Design, Heap (Priority Queue) https://leetcode.com/problems/design-twitter Medium 458 Array, Depth-First Search https://leetcode.com/problems/array-nesting Medium 459 Array, Math, Dynamic Programming, Game Theory https://leetcode.com/problems/stone-game Medium 460 Array, Hash Table https://leetcode.com/problems/degree-of-an-array Easy 461 Hash Table, String, Bit Manipulation, Sorting https://leetcode.com/problems/find-the-difference Easy 462 Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree https://leetcode.com/problems/minimum-absolute-difference-in-bst Easy 463 Array, Binary Search, Matrix https://leetcode.com/problems/count-negative-numbers-in-a-sorted-matrix Easy 464 Array, Greedy, Heap (Priority Queue) https://leetcode.com/problems/course-schedule-iii Hard 465 Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes Medium 466 Array, Matrix, Simulation https://leetcode.com/problems/reshape-the-matrix Easy 467 Array, Matrix https://leetcode.com/problems/toeplitz-matrix Easy 468 Dynamic Programming https://leetcode.com/problems/knight-probability-in-chessboard Medium 469 Array, Two Pointers, Binary Search, Sorting https://leetcode.com/problems/find-k-th-smallest-pair-distance Hard 470 Design, Segment Tree, Ordered Set https://leetcode.com/problems/my-calendar-i Medium 471 String, Dynamic Programming https://leetcode.com/problems/minimum-ascii-delete-sum-for-two-strings Medium 472 Array, Breadth-First Search, Matrix https://leetcode.com/problems/shortest-path-in-a-grid-with-obstacles-elimination Hard 473 Array, Design, Prefix Sum https://leetcode.com/problems/range-sum-query-immutable Easy 474 Tree, Breadth-First Search, Binary Tree https://leetcode.com/problems/check-completeness-of-a-binary-tree Medium 475 Array https://leetcode.com/problems/maximize-distance-to-closest-person Medium 476 Stack, Design, Queue https://leetcode.com/problems/implement-stack-using-queues Easy 477 Math, Dynamic Programming, Bit Manipulation, Memoization, Game Theory, Bitmask https://leetcode.com/problems/can-i-win Medium 478 Hash Table, String, Sorting https://leetcode.com/problems/custom-sort-string Medium 479 Array, Hash Table https://leetcode.com/problems/brick-wall Medium 480 Array, Hash Table, Stack, Monotonic Stack https://leetcode.com/problems/next-greater-element-i Easy 481 Tree, Depth-First Search, Binary Tree https://leetcode.com/problems/sum-of-root-to-leaf-binary-numbers Easy 482 Depth-First Search, Breadth-First Search, Graph, Topological Sort https://leetcode.com/problems/find-eventual-safe-states Medium 483 Array, Queue, Sorting, Simulation https://leetcode.com/problems/reveal-cards-in-increasing-order Medium 484 Array, String, Dynamic Programming, Depth-First Search, Trie https://leetcode.com/problems/concatenated-words Hard 485 Array, Two Pointers, Greedy, Sorting https://leetcode.com/problems/boats-to-save-people Medium 486 Array, Hash Table, Divide and Conquer, Tree, Binary Tree https://leetcode.com/problems/construct-binary-tree-from-preorder-and-postorder-traversal Medium 487 Array, Dynamic Programming, Binary Indexed Tree https://leetcode.com/problems/count-number-of-teams Medium 488 Hash Table, String, Bit Manipulation, Sliding Window, Rolling Hash, Hash Function https://leetcode.com/problems/repeated-dna-sequences Medium 489 Hash Table, String, Sliding Window https://leetcode.com/problems/substring-with-concatenation-of-all-words Hard 490 Array, Hash Table, Breadth-First Search https://leetcode.com/problems/bus-routes Hard 491 Array, Hash Table, String https://leetcode.com/problems/find-and-replace-pattern Medium 492 Array, Binary Search, Depth-First Search, Breadth-First Search, Union Find, Heap (Priority Queue), Matrix https://leetcode.com/problems/swim-in-rising-water Hard 493 Depth-First Search, Breadth-First Search, Union Find, Graph https://leetcode.com/problems/number-of-operations-to-make-network-connected Medium 494 Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort https://leetcode.com/problems/sort-an-array Medium 495 Array, Backtracking, Matrix https://leetcode.com/problems/path-with-maximum-gold Medium 496 Array, Hash Table, Bit Manipulation, Sorting https://leetcode.com/problems/set-mismatch Easy 497 Linked List https://leetcode.com/problems/split-linked-list-in-parts Medium 498 Array, Two Pointers, Dynamic Programming, Enumeration https://leetcode.com/problems/longest-mountain-in-array Medium 499 String, String Matching https://leetcode.com/problems/rotate-string Easy 500 Array, Hash Table, String https://leetcode.com/problems/unique-email-addresses Easy