Merge pull request #1369 from eunice-hong/main

[eunice-hong] WEEK 4 Solutions

Author: eunice-hong

coin-change/eunice-hong.ts

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+
+/**
+ * 
+ * Time Complexity: O(n * amount)
+ * Space Complexity: O(amount)
+ */
+function coinChange(coins: number[], amount: number): number {
+  // Initialize dp array with Infinity
+  const dp = new Array(amount + 1).fill(Infinity);
+  // Base case: 0 coins needed to make amount 0
+  dp[0] = 0;
+
+  // Iterate through each coin
+  for (let coin of coins) {
+    // Update dp array for each amount from coin to amount
+    for (let i = coin; i <= amount; i++) {
+      // Choose the minimum between current dp[i] and dp[i - coin] + 1
+      dp[i] = Math.min(dp[i], dp[i - coin] + 1);
+    }
+  }
+
+  // If dp[amount] is still Infinity, it means it's not possible to make the amount
+  return dp[amount] === Infinity ? -1 : dp[amount];
+}

find-minimum-in-rotated-sorted-array/eunice-hong.ts

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+
+/**
+ * 
+ * Time Complexity: O(n)
+ * Space Complexity: O(1)
+ */
+function findMin(nums: number[]): number {
+    let index = 0;
+    // find the index of where the value is greater than the next value
+    while (nums[index] < nums[(index + 1) % nums.length]) {
+      index++;
+    }
+    // return the next value
+    return nums[(index + 1) % nums.length]
+};

maximum-depth-of-binary-tree/eunice-hong.ts

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+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+/**
+ * 
+ * Time Complexity: O(n)
+ * Space Complexity: O(n)
+ */
+function maxDepth(root: TreeNode | null): number {
+    if (!root) {
+        // tree is empty
+        return 0
+    } else if (!root.left && !root.right) {
+        // tree has no children
+        return 1
+    } else {
+        // tree has at least one child
+        return 1 + Math.max(maxDepth(root.left), maxDepth(root.right))
+    }
+};

merge-two-sorted-lists/eunice-hong.ts

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+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+/**
+ * 
+ * Time Complexity: O(n + m)
+ * Space Complexity: O(n + m)
+ */
+function mergeTwoLists(list1: ListNode | null, list2: ListNode | null): ListNode | null {
+    if (!list1 && !list2) {
+        // both lists are empty
+        return null
+    } else if (!list1) {
+        // list1 is empty
+        return list2
+    } else if (!list2) {
+        // list2 is empty
+        return list1
+    } else if (list1.val <= list2.val) {
+        // list1's current node is smaller
+        return new ListNode(list1.val, mergeTwoLists(list1.next, list2))
+    } else {
+        // list2's current node is smaller
+        return new ListNode(list2.val, mergeTwoLists(list1, list2.next))
+    }
+};

word-search/eunice-hong.ts

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+
+/**
+ * Time Complexity: O(m * n * 4^k)
+ * Space Complexity: O(m * n)
+ */
+function exist(board: string[][], word: string): boolean {
+  // Initialize the board dimensions
+  const m = board.length;
+  const n = board[0].length;
+
+  const dfs = (i: number, j: number, index: number): boolean => {
+    // If we've matched all characters, return true
+    if (index === word.length) return true;
+    // If out of bounds or current character doesn't match, return false
+    if (i < 0 || i >= m || j < 0 || j >= n || board[i][j] !== word[index]) return false;
+
+    // Temporarily mark the current cell as visited
+    const temp = board[i][j];
+    board[i][j] = '#';
+
+    // Explore all four possible directions
+    const found =
+      dfs(i + 1, j, index + 1) ||
+      dfs(i - 1, j, index + 1) ||
+      dfs(i, j + 1, index + 1) ||
+      dfs(i, j - 1, index + 1);
+
+    // Unmark the current cell (backtracking)
+    board[i][j] = temp;
+
+    // Return true if we found the word
+    return found;
+  };
+
+  // Iterate through each cell in the board
+  for (let i = 0; i < m; i++) {
+    for (let j = 0; j < n; j++) {
+      // Start DFS from each cell
+      if (dfs(i, j, 0)) return true;
+    }
+  }
+
+  // If we didn't find the word, return false
+  return false;
+}