🧩 LeetCode Practice

This folder contains my solutions to various LeetCode problems, written in C++.
I’m solving at least one problem regularly to improve problem-solving and coding skills.

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📅 Progress Log

✅ Problem 46: Permutations

• Link: LeetCode 46. Permutations
• Solution file: 46_permutations.cpp
• Concepts used: Recursion, Backtracking
• Time Complexity: O(n * n!)
• Space Complexity: O(n!) (recursion stack)

✅ Problem 37: Sudoku Solver

• Link: LeetCode 37. Sudoku Solver
• Solution file: 37_sudoku_solver.cpp
• Concepts used: Backtracking, Constraint Satisfaction
• Time Complexity: O(9^(n*n)) in worst case (pruned heavily by constraints)
• Space Complexity: O(n^2) for the board state

✅ Problem 125: Valid Palindrome

• Link: LeetCode 125. Valid Palindrome
• Solution file: 125_valid_palindrome.cpp
• Concepts used: Two Pointers, String Manipulation
• Time Complexity: O(n)
• Space Complexity: O(1)

✅ Problem 1910: Remove All Occurrences of a Substring

• Link: LeetCode 1910. Remove All Occurrences of a Substring
• Solution file: 1910_remove_all_occurrences_of_a_substring.cpp
• Concepts used: String, Erase, Substring Search
• Time Complexity: O(n * m) (worst case, where n = length of string, m = length of substring)
• Space Complexity: O(1)

✅ Problem 344: Reverse String

• Link: LeetCode 344. Reverse String
• Solution file: 344_reverse_string.cpp
• Concepts used: Two Pointers, Array Manipulation
• Time Complexity: O(n)
• Space Complexity: O(1)

✅ Problem 443: String Compression

• Link: LeetCode 443. String Compression
• Solution file: 443_string_compression.cpp
• Concepts used: Two Pointers, String manipulation
• Time Complexity: O(n)
• Space Complexity: O(1)

✅ Problem 151: Reverse Words in a String

• Link: LeetCode 151. Reverse Words in a String
• Solution file: 151_reverse_words_in_a_string.cpp
• Concepts used: String, Two Pointers, Trimming spaces
• Time Complexity: O(n)
• Space Complexity: O(n) (for storing result)

✅ Problem 567: Permutation in String

• Link: LeetCode 567. Permutation in String
• Solution file: 567_permutation_in_string.cpp
• Concepts used: Sliding Window, Hashing
• Time Complexity: O(n)
• Space Complexity: O(1) (fixed array size 26 for characters)

✅ Problem 34: Find First and Last Position of Element in Sorted Array

• Link: LeetCode 34. Find First and Last Position of Element in Sorted Array
• Solution file: 34_find_first_and_last_position.cpp
• Concepts used: Binary Search
• Time Complexity: O(log n)
• Space Complexity: O(1)

✅ Problem 16: 3Sum Closest

• Link: LeetCode 16. 3Sum Closest
• Solution file: 16_3sum_closest.cpp
• Concepts used: Sorting, Two Pointers
• Time Complexity: O(n^2)
• Space Complexity: O(1)

✅ Problem 26: Remove Duplicates from Sorted Array

• Link: LeetCode 26. Remove Duplicates from Sorted Array
• Solution file: 26_remove_duplicates.cpp
• Concepts used: Two Pointers
• Time Complexity: O(n)
• Space Complexity: O(1)

✅ Problem 27: Remove Element

• Link: LeetCode 27. Remove Element
• Solution file: 27_remove_element.cpp
• Concepts used: Two Pointers, Array manipulation
• Time Complexity: O(n)
• Space Complexity: O(1)

✅ Problem 3516: Find Closest Person

• Link: [LeetCode 3516. Find Closest Person]([(https://leetcode.com/problems/find-closest-person/)]
• Solution file: 3516_closest_person.cpp
• Concepts used: Math
• Time Complexity: O(1)
• Space Complexity: O(1)

✅ Problem 69: Sqrt(x)

• Link: LeetCode 69. Sqrt(x)
• Solution file: 69_sqrtx.cpp
• Concepts used: Binary Search
• Time Complexity: O(log n)
• Space Complexity: O(1)

✅ Problem 75: Sort Colors

• Link: LeetCode 75. Sort Colors
• Solution file: 75_sort_colors.cpp
• Concepts used: Three Pointers, Dutch National Flag Algorithm
• Time Complexity: O(n)
• Space Complexity: O(1)

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🔮 Goals

• Solve problems daily to strengthen DSA & problem-solving skills
• Document my journey for future reference
• Build a strong LeetCode streak and prep for interviews

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🛠️ Tech Used

• C++
• Git & GitHub
• VSCode