Medium

Ad hoc

Easy

• 1. Two Sum - Solution
• 9. Palindrome Number - Solution
• 26. Remove Duplicates from Sorted Array - Solution
• 27. Remove Element - Solution
• 506. Relative Ranks - Solution
• 2485. Find the Pivot Integer - Solution

Medium

• 452. Minimum Number of Arrows to Burst Balloons - Solution
• 3075. Maximize Happiness of Selected Children - Solution

String

• 13. Roman to Integer - Solution
• 14. Longest Common Prefix - Solution
• 58. Length of Last Word - Solution
• 205. Isomorphic Strings - Solution
• 2000. Reverse Prefix of Word - Solution

Stack, Queue

Easy

• 20. Valid Parentheses - Solution
• 1544. Make The String Great - Solution
• 1614. Maximum Nesting Depth of the Parentheses - Solution
• 1700. Number of Students Unable to Eat Lunch - Solution
• 2073. Time Needed to Buy Tickets - Solution

Medium

• 200. Number of Islands - Solution
• 402. Remove K Digits - Solution
• 678. Valid Parenthesis String - Solution
• 950. Reveal Cards In Increasing Order - Solution

Hash table

Easy

• 169. Majority Element - Solution
• 205. Isomorphic Strings - Solution
• 2441. Largest Positive Integer That Exists With Its Negative - Solution

Medium

• 287. Find the Duplicate Number - Solution
• 442. Find All Duplicates in an Array - Solution
• 2997. Minimum Number of Operations to Make Array XOR Equal to K - Solution

Hard

• 41. First Missing Positive - Solution
• 752. Open the Lock - Solution
• 1915. Number of Wonderful Substrings - Solution

Linked List

Easy

• 21. Merge Two Sorted Lists - Solution

Medium

• 2. Add Two Numbers - Solution
• 237. Delete Node in a Linked List - Solution
• 2487. Remove Nodes From Linked List - Solution
• 2816. Double a Number Represented as a Linked List - Solution

Prefix sum

Easy

• 2485. Find the Pivot Integer - Solution

Medium

• 1915. Number of Wonderful Substrings - Solution

DFS, BFS

Easy

• 463. Island Perimeter - Solution

Medium

• 79. Word Search - Solution
• 752. Open the Lock - Solution
• 1219. Path with Maximum Gold - Solution
• 1249. Minimum Remove to Make Valid Parentheses - Solution

Hard

• 979. Distribute Coins in Binary Tree - Solution
• 988. Smallest String Starting From Leaf - Solution

Two-pointers

Easy

• 88. Merge Sorted Array - Solution

Medium

• 165. Compare Version Numbers - Solution
• 881. Boats to Save People - Solution
• 2997. Minimum Number of Operations to Make Array XOR Equal to K - Solution

Hard

• 786. K-th Smallest Prime Fraction - Solution (Binary search tree, Heap, Two-pointers)
• 42. Trapping Rain Water - Solution (Dynamic programming)

Sliding window (Medium)

• 209. Minimum Size Subarray Sum - Solution

• 713. Subarray Product Less Than K - Solution

• 992. Subarrays with K Different Integers - Solution

• 1248. Count Number of Nice Subarrays - Solution

• 2444. Count Subarrays With Fixed Bounds - Solution

• 2958. Length of Longest Subarray With at Most K Frequency - Solution

• 2962. Count Subarrays Where Max Element Appears at Least K Times - Solution

• 1052. Grumpy Bookstore Owner - Solution

Heap (Priority Queue)

Medium

• 786. K-th Smallest Prime Fraction - Solution (Binary search tree, Heap, Two-pointers)

Hard

• 857. Minimum Cost to Hire K Workers - Solution
• 2812. Find the Safest Path in a Grid - Solution (Heap, Binary Search, BFS)

Tree

Easy

• 404. Sum of Left Leaves - Solution
• 2331. Evaluate Boolean Binary Tree - Solution

Medium

• 623. Add One Row to Tree - Solution
• 979. Distribute Coins in Binary Tree - Solution
• 988. Smallest String Starting From Leaf - Solution
• 1325. Delete Leaves With a Given Value - Solution
• 1382. Balance a Binary Search Tree - Solution

Hard

• 786. K-th Smallest Prime Fraction - Solution (Binary search tree, Heap, Two-pointers)

Graph

Easy

• 1971. Find if Path Exists in Graph - Solution

Medium

• 29. Sum Root to Leaf Numbers - Solution
• 310. Minimum Height Trees - Solution

Hard

• 834. Sum of Distances in Tree - Solution (DP)

Matrix (2-dimensions)

Easy

• 463. Island Perimeter - Solution
• 2373. Largest Local Values in a Matrix - Solution

Medium

• 79. Word Search - Solution
• 200. Number of Islands - Solution
• 861. Score After Flipping Matrix - Solution
• 1219. Path with Maximum Gold - Solution
• 1992. Find All Groups of Farmland - Solution

Hard

• 2812. Find the Safest Path in a Grid - Solution (Heap, Binary Search, BFS)
• 1289. Minimum Falling Path Sum II - Solution(DP)

Dynamic programming

Easy

• 1137. N-th Tribonacci Number - Solution

Medium

• 678. Valid Parenthesis String - Solution
• 2370. Longest Ideal Subsequence - Solution

Hard

• 42. Trapping Rain Water - Solution(Two Pointers)
• 85. Maximal Rectangle - Solution (Histogram)
• 514. Freedom Trail - Solution
• 834. Sum of Distances in Tree - Solution (Graph, DFS)
• 1289. Minimum Falling Path Sum II - Solution(Matrix)

Bit Manipulation

• 287. Find the Duplicate Number - Solution
• 861. Score After Flipping Matrix - Solution
• 1915. Number of Wonderful Substrings - Solution

Histogram (Left min, right min)

• 84. Largest Rectangle in Histogram - Solution
• 85. Maximal Rectangle - Solution (DP)