LeetCode Questions List

LeetCode Questions List

This page contains a comprehensive list of all LeetCode problems solved in this blog, organized by difficulty level, category, and solution approach.

Summary Statistics

• Total Problems: 61
• Easy: 1 problem
• Medium: 56 problems
• Hard: 4 problems

All LeetCode Problems

Problem	Title	Difficulty	Category	Solution Approach	Date Added
3	Longest Substring Without Repeating Characters	Medium	String, Sliding Window	Hash Map, Two Pointers	2025-10-09
23	Swap Nodes in Pairs	Medium	Linked List	Recursion, Iteration	2025-09-24
25	Reverse Nodes in k-Group	Hard	Linked List	Recursion, Iteration	2025-09-24
33	Search in Rotated Sorted Array	Medium	Array, Binary Search	Binary Search	2025-09-23
46	Permutations	Medium	Backtracking, Recursion	Backtracking, STL	2025-10-21
47	Permutations II	Medium	Backtracking, Recursion, Duplicates	Backtracking, STL	2025-10-21
48	Rotate Image	Medium	Array, Matrix	Matrix Rotation	2025-09-24
50	Pow(x, n)	Medium	Math, Recursion	Fast Exponentiation	2025-09-25
54	Spiral Matrix	Medium	Array, Matrix	Simulation	2025-09-25
62	Unique Paths	Medium	Math, Dynamic Programming	DP, Combinatorics	2025-09-24
77	Combinations	Medium	Backtracking, Recursion	Backtracking, DFS	2025-10-20
84	Largest Rectangle in Histogram	Hard	Stack, Monotonic Stack	Monotonic Stack	2025-10-21
89	Gray Code	Medium	Math, Bit Manipulation	Bit Manipulation	2025-09-25
96	Unique Binary Search Trees	Medium	Math, Dynamic Programming	DP, Catalan Numbers	2025-10-03
131	Palindrome Partitioning	Medium	Backtracking	Backtracking, DFS	2025-09-30
133	Clone Graph	Medium	Graph, DFS, BFS	DFS, BFS, Deep Copy	2025-10-20
150	Evaluate Reverse Polish Notation	Medium	Stack	Stack	2025-09-24
207	Course Schedule	Medium	Graph, Topological Sort	Topological Sort, Cycle Detection	2025-10-21
218	The Skyline Problem	Hard	Array, Sweep Line	Sweep Line, Priority Queue	2025-10-05
240	Search a 2D Matrix II	Medium	Array, Binary Search	Binary Search, Divide & Conquer	2025-10-07
300	Longest Increasing Subsequence	Medium	Array, Dynamic Programming	DP, Binary Search	2025-10-17
314	Binary Tree Vertical Order Traversal	Medium	Tree, BFS	BFS, Vertical Order	2025-10-21
316	Remove Duplicate Letters	Medium	String, Stack	Monotonic Stack, Greedy	2025-10-17
317	Shortest Distance from All Buildings	Hard	BFS, Matrix	BFS, Multi-source	2025-09-24
322	Coin Change	Medium	Dynamic Programming, DP	DP, Unbounded Knapsack	2025-10-21
347	Top K Frequent Elements	Medium	Array, Hash Table, Heap	Bucket Sort, Quickselect, Heap	2025-10-21
348	Design Tic-Tac-Toe	Medium	Design, Array	Counter Optimization, State Tracking	2025-10-21
394	Decode String	Medium	String, Stack	Stack, String Processing	2025-10-19
406	Queue Reconstruction by Height	Medium	Array, Greedy	Greedy, Sorting	2025-10-19
417	Pacific Atlantic Water Flow	Medium	Array, DFS	DFS, BFS	2025-10-19
419	Battleships in a Board	Medium	Array, Matrix	Top-Left Corner, DFS	2025-10-21
426	Convert Binary Search Tree to Sorted Doubly Linked List	Medium	Tree, Linked List, DFS	Inorder Traversal, Recursion	2025-10-22
437	Path Sum III	Medium	Tree, DFS	DFS, Recursion	2025-10-19
494	Target Sum	Medium	Array, Dynamic Programming	DP, Subset Sum	2025-10-15
636	Exclusive Time of Functions	Medium	Stack, Parsing	Stack, Log Parsing	2025-10-27
708	Insert into a Sorted Circular Linked List	Medium	Linked List, Circular	Two Pointers, Iteration	2025-10-27
863	All Nodes Distance K in Binary Tree	Medium	Tree, DFS, BFS	Graph Conversion, DFS, Parent Pointer	2025-10-25
503	Next Greater Element II	Medium	Array, Stack	Monotonic Stack	2025-10-17
545	Boundary of Binary Tree	Medium	Tree, DFS	DFS, Boundary Traversal	2025-10-21
648	Replace Words	Medium	String, Trie	Trie, Hash Set	2025-10-17
695	Max Area of Island	Medium	DFS, Graph, Matrix	DFS, Connected Components	2025-10-21
752	Open the Lock	Medium	BFS, Shortest Path	BFS, State Space	2025-10-21
794	Valid Tic-Tac-Toe State	Medium	Array, String	Simulation, Validation	2025-09-24
912	Sort an Array	Medium	Array, Sorting	Merge Sort, Heap Sort, Counting Sort	2025-10-06
973	K Closest Points to Origin	Medium	Array, Sorting, Heap	Sorting, Heap, Quickselect	2025-10-21
990	Satisfiability of Equality Equations	Medium	Union Find, Graph	Union Find, DFS	2025-10-04
1094	Car Pooling	Medium	Array, Sorting, Simulation	Bucket Sort, Event Processing	2025-10-22
1124	Longest Well-Performing Interval	Medium	Array, Hash Table	Hash Map, Prefix Sum	2025-10-16
1207	Unique Number of Occurrences	Easy	Array, Hash Table	Hash Map, Hash Set	2025-10-20
1242	Web Crawler Multithreaded	Medium	Concurrency, Multithreading	Multithreading, BFS	2025-09-24
1249	Minimum Remove to Make Valid Parentheses	Medium	String, Stack	Stack Validation, Parentheses	2025-10-22
1443	Minimum Time to Collect All Apples in a Tree	Medium	Tree, DFS, BFS	DFS, Tree Traversal	2025-10-21
1570	Dot Product of Two Sparse Vectors	Medium	Hash Map, Data Structure	Hash Map, Optimization	2025-10-19
1650	Lowest Common Ancestor of a Binary Tree III	Medium	Tree, Binary Tree, LCA	Two Pointers, Tree Traversal	2025-10-21
1856	Maximum Sum of Minimum Product	Medium	Array, Stack	Monotonic Stack, Prefix Sum	2025-10-17
1865	Finding Pairs With a Certain Sum	Medium	Hash Map, Data Structure	Hash Map, Count Tracking	2025-10-19
1868	Product of Two Run-Length Encoded Arrays	Medium	Run-Length Encoding, Two Pointers	Two Pointers, Array Processing	2025-10-21
2043	Simple Bank System	Medium	Design, Data Structure	Data Structure Design	2025-10-21
2466	Count Ways To Build Good Strings	Medium	Dynamic Programming	DP, Bottom-up, Top-down	2025-10-16
2799	Count Complete Subarrays in an Array	Medium	Array, Sliding Window	Sliding Window, Hash Map	2025-10-17

Problems by Difficulty

Easy (1 problem)

• 1207. Unique Number of Occurrences

Medium (56 problems)

• 3. Longest Substring Without Repeating Characters
• 23. Swap Nodes in Pairs
• 33. Search in Rotated Sorted Array
• 46. Permutations
• 47. Permutations II
• 48. Rotate Image
• 394. Decode String
• 50. Pow(x, n)
• 54. Spiral Matrix
• 62. Unique Paths
• 695. Max Area of Island
• 77. Combinations
• 89. Gray Code
• 96. Unique Binary Search Trees
• 131. Palindrome Partitioning
• 1443. Minimum Time to Collect All Apples in a Tree
• 1650. Lowest Common Ancestor of a Binary Tree III
• 150. Evaluate Reverse Polish Notation
• 240. Search a 2D Matrix II
• 300. Longest Increasing Subsequence
• 316. Remove Duplicate Letters
• 406. Queue Reconstruction by Height
• 417. Pacific Atlantic Water Flow
• 437. Path Sum III
• 494. Target Sum
• 503. Next Greater Element II
• 636. Exclusive Time of Functions
• 648. Replace Words
• 708. Insert into a Sorted Circular Linked List
• 863. All Nodes Distance K in Binary Tree
• 912. Sort an Array
• 990. Satisfiability of Equality Equations
• 1124. Longest Well-Performing Interval
• 1242. Web Crawler Multithreaded
• 1570. Dot Product of Two Sparse Vectors
• 1856. Maximum Sum of Minimum Product
• 1865. Finding Pairs With a Certain Sum
• 1868. Product of Two Run-Length Encoded Arrays
• 2043. Simple Bank System
• 2466. Count Ways To Build Good Strings
• 2799. Count Complete Subarrays in an Array
• 794. Valid Tic-Tac-Toe State
• 973. K Closest Points to Origin

Hard (4 problems)

• 25. Reverse Nodes in k-Group
• 84. Largest Rectangle in Histogram
• 218. The Skyline Problem
• 317. Shortest Distance from All Buildings

Problems by Category

Array & Matrix

• 33. Search in Rotated Sorted Array - Binary Search
• 48. Rotate Image - Matrix Rotation
• 54. Spiral Matrix - Simulation
• 62. Unique Paths - DP, Combinatorics
• 695. Max Area of Island - DFS, Connected Components
• 240. Search a 2D Matrix II - Binary Search, Divide & Conquer
• 300. Longest Increasing Subsequence - DP, Binary Search
• 406. Queue Reconstruction by Height - Greedy, Sorting
• 417. Pacific Atlantic Water Flow - DFS, BFS
• 494. Target Sum - DP, Subset Sum
• 503. Next Greater Element II - Monotonic Stack
• 912. Sort an Array - Merge Sort, Heap Sort, Counting Sort
• 1124. Longest Well-Performing Interval - Hash Map, Prefix Sum
• 1856. Maximum Sum of Minimum Product - Monotonic Stack, Prefix Sum
• 2799. Count Complete Subarrays in an Array - Sliding Window, Hash Map
• 1094. Car Pooling - Bucket Sort, Event Processing
• 1207. Unique Number of Occurrences - Hash Map, Hash Set
• 347. Top K Frequent Elements - Bucket Sort, Quickselect, Heap
• 419. Battleships in a Board - Top-Left Corner, DFS
• 973. K Closest Points to Origin - Sorting, Heap, Quickselect

String Processing

• 3. Longest Substring Without Repeating Characters - Hash Map, Two Pointers
• 316. Remove Duplicate Letters - Monotonic Stack, Greedy
• 394. Decode String - Stack, String Processing
• 648. Replace Words - Trie, Hash Set
• 794. Valid Tic-Tac-Toe State - Simulation, Validation
• 1249. Minimum Remove to Make Valid Parentheses - Stack Validation, Parentheses

Linked List

• 23. Swap Nodes in Pairs - Recursion, Iteration
• 25. Reverse Nodes in k-Group - Recursion, Iteration
• 708. Insert into a Sorted Circular Linked List - Two Pointers, Circular List

Tree & DFS

• 314. Binary Tree Vertical Order Traversal - BFS, Level Order
• 426. Convert Binary Search Tree to Sorted Doubly Linked List - Inorder Traversal, Recursion
• 437. Path Sum III - DFS, Recursion
• 545. Boundary of Binary Tree - DFS, Boundary Traversal
• 863. All Nodes Distance K in Binary Tree - Graph Conversion, DFS, Parent Pointer
• 1443. Minimum Time to Collect All Apples in a Tree - DFS, Tree Traversal
• 1650. Lowest Common Ancestor of a Binary Tree III - Two Pointers, Tree Traversal

Dynamic Programming

• 62. Unique Paths - DP, Combinatorics
• 96. Unique Binary Search Trees - DP, Catalan Numbers
• 300. Longest Increasing Subsequence - DP, Binary Search
• 494. Target Sum - DP, Subset Sum
• 2466. Count Ways To Build Good Strings - DP, Bottom-up, Top-down

Backtracking

• 46. Permutations - Backtracking, STL
• 47. Permutations II - Backtracking, STL, Duplicates
• 77. Combinations - Backtracking
• 131. Palindrome Partitioning - Backtracking, DFS

Stack & Queue

• 84. Largest Rectangle in Histogram - Monotonic Stack
• 150. Evaluate Reverse Polish Notation - Stack
• 316. Remove Duplicate Letters - Monotonic Stack, Greedy
• 636. Exclusive Time of Functions - Stack, Log Parsing
• 503. Next Greater Element II - Monotonic Stack
• 1856. Maximum Sum of Minimum Product - Monotonic Stack, Prefix Sum

Graph & Union Find

• 417. Pacific Atlantic Water Flow - DFS, BFS
• 863. All Nodes Distance K in Binary Tree - Graph Conversion, DFS, Parent Pointer
• 990. Satisfiability of Equality Equations - Union Find, DFS
• 317. Shortest Distance from All Buildings - BFS, Multi-source

Data Structure Design

• 1570. Dot Product of Two Sparse Vectors - Hash Map, Optimization
• 1865. Finding Pairs With a Certain Sum - Hash Map, Count Tracking
• 2043. Simple Bank System - Data Structure Design
• 348. Design Tic-Tac-Toe - Counter Optimization, State Tracking

Advanced Algorithms

• 218. The Skyline Problem - Sweep Line, Priority Queue
• 1242. Web Crawler Multithreaded - Multithreading, BFS

Math & Bit Manipulation

• 50. Pow(x, n) - Fast Exponentiation
• 89. Gray Code - Bit Manipulation

Run-Length Encoding

• 1868. Product of Two Run-Length Encoded Arrays - Two Pointers, Array Processing

Solution Approaches Summary

Most Common Approaches

1. Dynamic Programming (DP) - 5 problems
2. Monotonic Stack - 4 problems
3. Binary Search - 4 problems
4. Hash Map/Set - 6 problems
5. DFS/BFS - 5 problems
6. Backtracking - 2 problems
7. Sliding Window - 2 problems
8. Two Pointers - 2 problems
9. Trie - 1 problem
10. Union Find - 1 problem
11. Sweep Line - 1 problem
12. Data Structure Design - 2 problems

Algorithm Patterns

• Array Processing: Sliding window, two pointers, prefix sum
• String Processing: Trie, hash map, monotonic stack
• Graph Traversal: DFS, BFS, Union Find
• Optimization: Dynamic programming, greedy algorithms
• Data Structures: Stack, queue, heap, trie
• Search: Binary search, divide and conquer

Recent Additions

Latest Problems (October 2025)

• 636. Exclusive Time of Functions - Stack, Log Parsing
• 708. Insert into a Sorted Circular Linked List - Two Pointers, Circular List
• 863. All Nodes Distance K in Binary Tree - Graph Conversion, DFS, Parent Pointer
• 1249. Minimum Remove to Make Valid Parentheses - Stack Validation, Parentheses
• 426. Convert Binary Search Tree to Sorted Doubly Linked List - Inorder Traversal, Recursion
• 1094. Car Pooling - Bucket Sort, Event Processing
• 1207. Unique Number of Occurrences - Hash Map, Hash Set
• 348. Design Tic-Tac-Toe - Counter Optimization, State Tracking
• 419. Battleships in a Board - Top-Left Corner, DFS
• 545. Boundary of Binary Tree - DFS, Boundary Traversal
• 347. Top K Frequent Elements - Bucket Sort, Quickselect, Heap
• 973. K Closest Points to Origin - Sorting, Heap, Quickselect
• 207. Course Schedule - Topological Sort, Cycle Detection
• 133. Clone Graph - DFS, BFS, Deep Copy
• 752. Open the Lock - BFS, Shortest Path
• 314. Binary Tree Vertical Order Traversal - BFS, Vertical Order
• 322. Coin Change - DP, Unbounded Knapsack
• 77. Combinations - Backtracking, DFS
• 47. Permutations II - Backtracking, STL, Duplicates
• 46. Permutations - Backtracking, STL
• 1650. Lowest Common Ancestor of a Binary Tree III - Two Pointers, Tree Traversal
• 2043. Simple Bank System - Data Structure Design
• 1443. Minimum Time to Collect All Apples in a Tree - DFS, Tree Traversal
• 84. Largest Rectangle in Histogram - Monotonic Stack
• 695. Max Area of Island - DFS, Connected Components
• 1868. Product of Two Run-Length Encoded Arrays - Two Pointers, Array Processing
• 1865. Finding Pairs With a Certain Sum - Hash Map, Count Tracking
• 1570. Dot Product of Two Sparse Vectors - Hash Map, Optimization
• 437. Path Sum III - DFS, Recursion
• 394. Decode String - Stack, String Processing
• 417. Pacific Atlantic Water Flow - DFS, BFS
• 406. Queue Reconstruction by Height - Greedy, Sorting

Tips for Problem Solving

1. Identify the Pattern: Look for common algorithm patterns (DP, sliding window, etc.)
2. Start Simple: Begin with brute force, then optimize
3. Use Data Structures: Choose appropriate DS for the problem
4. Consider Edge Cases: Handle boundary conditions
5. Optimize Space/Time: Trade-offs between complexity and efficiency

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Last updated: October 27, 2025 Total problems solved: 61