Скачать или смотреть LEETCODE PROBLEMS 1-100 . C++ SOLUTIONS

Arrays and Two Pointers
1. Two Sum – Use hashmap to find complement in one pass.
26. Remove Duplicates from Sorted Array – Use two pointers to overwrite duplicates.
27. Remove Element – Shift non-target values to front with a write pointer.
80. Remove Duplicates II – Like #26 but allow at most two duplicates.
88. Merge Sorted Array – Merge in-place from the end using two pointers.
283. Move Zeroes – Shift non-zero values forward; fill the rest with zeros.



Sliding Window
3. Longest Substring Without Repeating Characters – Use hashmap and sliding window.
76. Minimum Window Substring – Track char frequency with two maps and a moving window.



Binary Search and Sorted Arrays
33. Search in Rotated Sorted Array – Modified binary search with pivot logic.
34. Find First and Last Position of Element – Binary search for left and right bounds.
35. Search Insert Position – Standard binary search for target or insertion point.
74. Search a 2D Matrix – Binary search treating matrix as a flat array.
81. Search in Rotated Sorted Array II – Extend #33 to handle duplicates.



Subarray Sums and Prefix Logic
53. Maximum Subarray – Kadane’s algorithm to track max current sum.
121. Best Time to Buy and Sell Stock – Track min price and update max profit.



Linked Lists
2. Add Two Numbers – Traverse two lists and simulate digit-by-digit addition.
19. Remove N-th Node From End – Use two pointers with a gap of n.
21. Merge Two Sorted Lists – Recursively or iteratively merge nodes.
23. Merge k Sorted Lists – Use min heap or divide-and-conquer merges.
24. Swap Nodes in Pairs – Recursively swap adjacent nodes.
25. Reverse Nodes in k-Group – Reverse sublists of size k using recursion.
61. Rotate List – Use length and modulo to rotate and relink.
82. Remove Duplicates II – Use dummy head and skip duplicates.
83. Remove Duplicates I – Traverse and skip repeated values.
86. Partition List – Create two lists based on x and connect them.



Stack
20. Valid Parentheses – Use stack to match open and close brackets.
84. Largest Rectangle in Histogram – Use monotonic stack to calculate max area.



Binary Trees
94. Binary Tree Inorder Traversal – DFS or use stack for in-order traversal.
98. Validate Binary Search Tree – Check value ranges recursively.
100. Same Tree – Compare values and structure recursively.
101. Symmetric Tree – Recursively compare mirrored subtrees.
102. Binary Tree Level Order Traversal – Use queue for BFS.
103. Binary Tree Zigzag Level Order – Modify BFS to alternate direction.
104. Maximum Depth of Binary Tree – DFS recursion to track max depth.
105. Build Tree from Preorder and Inorder – Recursively divide arrays.
106. Build Tree from Inorder and Postorder – Reverse of #105.
110. Balanced Binary Tree – DFS checking subtree heights, return early if unbalanced.



Backtracking
17. Letter Combinations of Phone Number – Map digits to letters and recurse.
22. Generate Parentheses – Use counts of open and close to generate valid strings.
39. Combination Sum – Use DFS to explore sum paths.
40. Combination Sum II – Sort and skip duplicates during recursion.
46. Permutations – Swap elements and recurse.
47. Permutations II – Like #46 but sort and skip duplicate values.
77. Combinations – DFS to select combinations of size k.
78. Subsets – Backtrack by including or excluding elements.
90. Subsets II – Sort and skip duplicates during subset generation.



Dynamic Programming
70. Climbing Stairs – DP similar to Fibonacci sequence.
198. House Robber – Track max value including or excluding current house.



Math and Bit Manipulation
136. Single Number – XOR all values to isolate the single one.
169. Majority Element – Use Boyer-Moore voting algorithm.



Hashing and Frequency Maps
49. Group Anagrams – Sort characters and group in hashmap.
128. Longest Consecutive Sequence – Use set to expand sequences.
242. Valid Anagram – Count characters using map or array.



Matrix and Miscellaneous
11. Container With Most Water – Two pointers moving inward.
42. Trapping Rain Water – Track left and right max heights with two pointers.
54. Spiral Matrix – Traverse matrix layer by layer.
73. Set Matrix Zeroes – Use first row and column as markers.



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