🧩 My LeetCode Solutions

Auto-synced from LeetCode and organized into a portfolio. Solutions live in solutions/; this README is regenerated on every sync by scripts/generate_stats.py.

📊 Summary

119 solved  ·  🟢 12 Easy  ·  🟡 100 Medium  ·  🔴 7 Hard

Last synced: 2026-08-06 10:23 UTC

✅ Problems

#	Problem	Difficulty	Topics	Languages
1	Two Sum	🟢 Easy	Array, Hash Table	Python
2	Add Two Numbers	🟡 Medium	Linked List, Math, Recursion	Python
3	Longest Substring Without Repeating Characters	🟡 Medium	Hash Table, String, Sliding Window	Python
5	Longest Palindromic Substring	🟡 Medium	Two Pointers, String, Dynamic Programming	Python
11	Container With Most Water	🟡 Medium	Array, Two Pointers, Greedy	Python
12	Integer to Roman	🟡 Medium	Hash Table, Math, String	Python
13	Roman to Integer	🟢 Easy	Hash Table, Math, String	Python
15	3Sum	🟡 Medium	Array, Two Pointers, Sorting	Python
20	Valid Parentheses	🟢 Easy	String, Stack	Python
22	Generate Parentheses	🟡 Medium	String, Dynamic Programming, Backtracking	Python
36	Valid Sudoku	🟡 Medium	Array, Hash Table, Matrix	Python
39	Combination Sum	🟡 Medium	Array, Backtracking	Python
40	Combination Sum II	🟡 Medium	Array, Backtracking	Python
42	Trapping Rain Water	🔴 Hard	Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack	Python
45	Jump Game II	🟡 Medium	Array, Dynamic Programming, Greedy	Python
48	Rotate Image	🟡 Medium	Array, Math, Matrix	Python
49	Group Anagrams	🟡 Medium	Array, Hash Table, String, Sorting	Python
53	Maximum Subarray	🟡 Medium	Array, Divide and Conquer, Dynamic Programming	Python
55	Jump Game	🟡 Medium	Array, Dynamic Programming, Greedy	Python
56	Merge Intervals	🟡 Medium	Array, Sorting	Python
57	Insert Interval	🟡 Medium	Array	Python
62	Unique Paths	🟡 Medium	Math, Dynamic Programming, Combinatorics	Python
63	Unique Paths II	🟡 Medium	Array, Dynamic Programming, Matrix	Python
64	Minimum Path Sum	🟡 Medium	Array, Dynamic Programming, Matrix	Python
70	Climbing Stairs	🟢 Easy	Math, Dynamic Programming, Memoization	Python
71	Simplify Path	🟡 Medium	String, Stack	Python
72	Edit Distance	🟡 Medium	String, Dynamic Programming	Python
78	Subsets	🟡 Medium	Array, Backtracking, Bit Manipulation	Python
79	Word Search	🟡 Medium	Array, String, Backtracking, Depth-First Search, Matrix	Python
91	Decode Ways	🟡 Medium	String, Dynamic Programming	Python
95	Unique Binary Search Trees II	🟡 Medium	Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree	Python
96	Unique Binary Search Trees	🟡 Medium	Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree	Python
97	Interleaving String	🟡 Medium	String, Dynamic Programming	Python
98	Validate Binary Search Tree	🟡 Medium	Tree, Depth-First Search, Binary Search Tree, Binary Tree	Python
102	Binary Tree Level Order Traversal	🟡 Medium	Tree, Breadth-First Search, Binary Tree	Python
120	Triangle	🟡 Medium	Array, Dynamic Programming	Python
121	Best Time to Buy and Sell Stock	🟢 Easy	Array, Dynamic Programming	Python
122	Best Time to Buy and Sell Stock II	🟡 Medium	Array, Dynamic Programming, Greedy	Python
128	Longest Consecutive Sequence	🟡 Medium	Array, Hash Table, Union-Find	Python
130	Surrounded Regions	🟡 Medium	Array, Depth-First Search, Breadth-First Search, Union-Find, Matrix	Python
131	Palindrome Partitioning	🟡 Medium	String, Dynamic Programming, Backtracking	Python
136	Single Number	🟢 Easy	Array, Bit Manipulation	Python
139	Word Break	🟡 Medium	Array, Hash Table, String, Dynamic Programming, Trie, Memoization	Python
140	Word Break II	🔴 Hard	Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization	Python
146	LRU Cache	🟡 Medium	Hash Table, Linked List, Design, Doubly-Linked List	Python
151	Reverse Words in a String	🟡 Medium	Two Pointers, String	Python
152	Maximum Product Subarray	🟡 Medium	Array, Dynamic Programming	Python
153	Find Minimum in Rotated Sorted Array	🟡 Medium	Array, Binary Search	Python
162	Find Peak Element	🟡 Medium	Array, Binary Search	Python
167	Two Sum II - Input Array Is Sorted	🟡 Medium	Array, Two Pointers, Binary Search	Python
191	Number of 1 Bits	🟢 Easy	Divide and Conquer, Bit Manipulation	Python
198	House Robber	🟡 Medium	Array, Dynamic Programming	Python
199	Binary Tree Right Side View	🟡 Medium	Tree, Depth-First Search, Breadth-First Search, Binary Tree	Python
200	Number of Islands	🟡 Medium	Array, Depth-First Search, Breadth-First Search, Union-Find, Matrix	Python
202	Happy Number	🟢 Easy	Hash Table, Math, Two Pointers	Python
207	Course Schedule	🟡 Medium	Depth-First Search, Breadth-First Search, Graph Theory, Topological Sort	Python
210	Course Schedule II	🟡 Medium	Depth-First Search, Breadth-First Search, Graph Theory, Topological Sort	Python
213	House Robber II	🟡 Medium	Array, Dynamic Programming	Python
230	Kth Smallest Element in a BST	🟡 Medium	Tree, Depth-First Search, Binary Search Tree, Binary Tree	Python
238	Product of Array Except Self	🟡 Medium	Array, Prefix Sum	Python
295	Find Median from Data Stream	🔴 Hard	Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream	Python
309	Best Time to Buy and Sell Stock with Cooldown	🟡 Medium	Array, Dynamic Programming	Python
310	Minimum Height Trees	🟡 Medium	Depth-First Search, Breadth-First Search, Graph Theory, Topological Sort	Python
322	Coin Change	🟡 Medium	Array, Dynamic Programming, Breadth-First Search	Python
329	Longest Increasing Path in a Matrix	🔴 Hard	Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph Theory, Topological Sort, Memoization, Matrix	Python
332	Reconstruct Itinerary	🔴 Hard	Array, String, Depth-First Search, Graph Theory, Sorting, Heap (Priority Queue), Eulerian Circuit	Python
338	Counting Bits	🟢 Easy	Dynamic Programming, Bit Manipulation	Python
347	Top K Frequent Elements	🟡 Medium	Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect	Python
355	Design Twitter	🟡 Medium	Hash Table, Linked List, Design, Heap (Priority Queue)	Python
394	Decode String	🟡 Medium	String, Stack, Recursion	Python
399	Evaluate Division	🟡 Medium	Array, String, Depth-First Search, Breadth-First Search, Union-Find, Graph Theory, Shortest Path	Python
417	Pacific Atlantic Water Flow	🟡 Medium	Array, Depth-First Search, Breadth-First Search, Matrix	Python
424	Longest Repeating Character Replacement	🟡 Medium	Hash Table, String, Sliding Window	Python
460	LFU Cache	🔴 Hard	Hash Table, Linked List, Design, Doubly-Linked List	Python
468	Validate IP Address	🟡 Medium	String	Python
498	Diagonal Traverse	🟡 Medium	Array, Matrix, Simulation	Python
547	Number of Provinces	🟡 Medium	Depth-First Search, Breadth-First Search, Union-Find, Graph Theory	Python
560	Subarray Sum Equals K	🟡 Medium	Array, Hash Table, Prefix Sum	Python
621	Task Scheduler	🟡 Medium	Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting	Python
622	Design Circular Queue	🟡 Medium	Array, Linked List, Design, Queue	Python
684	Redundant Connection	🟡 Medium	Depth-First Search, Breadth-First Search, Union-Find, Graph Theory	Python
695	Max Area of Island	🟡 Medium	Array, Depth-First Search, Breadth-First Search, Union-Find, Matrix	Python
718	Maximum Length of Repeated Subarray	🟡 Medium	Array, Binary Search, Dynamic Programming, Sliding Window, Rolling Hash, Hash Function	Python
721	Accounts Merge	🟡 Medium	Array, Hash Table, String, Depth-First Search, Breadth-First Search, Union-Find, Sorting	Python
743	Network Delay Time	🟡 Medium	Depth-First Search, Breadth-First Search, Graph Theory, Heap (Priority Queue), Shortest Path	Python
746	Min Cost Climbing Stairs	🟢 Easy	Array, Dynamic Programming	Python
785	Is Graph Bipartite?	🟡 Medium	Depth-First Search, Breadth-First Search, Union-Find, Graph Theory	Python
787	Cheapest Flights Within K Stops	🟡 Medium	Dynamic Programming, Depth-First Search, Breadth-First Search, Graph Theory, Heap (Priority Queue), Shortest Path	Python
797	All Paths From Source to Target	🟡 Medium	Backtracking, Depth-First Search, Breadth-First Search, Graph Theory	Python
802	Find Eventual Safe States	🟡 Medium	Depth-First Search, Breadth-First Search, Graph Theory, Topological Sort	Python
809	Expressive Words	🟡 Medium	Array, Two Pointers, String	Python
841	Keys and Rooms	🟡 Medium	Depth-First Search, Breadth-First Search, Graph Theory	Python
863	All Nodes Distance K in Binary Tree	🟡 Medium	Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree	Python
875	Koko Eating Bananas	🟡 Medium	Array, Binary Search	Python
886	Possible Bipartition	🟡 Medium	Depth-First Search, Breadth-First Search, Union-Find, Graph Theory	Python
947	Most Stones Removed with Same Row or Column	🟡 Medium	Hash Table, Depth-First Search, Union-Find, Graph Theory	Python
990	Satisfiability of Equality Equations	🟡 Medium	Array, String, Union-Find, Graph Theory	Python
994	Rotting Oranges	🟡 Medium	Array, Breadth-First Search, Matrix	Python
1004	Max Consecutive Ones III	🟡 Medium	Array, Binary Search, Sliding Window, Prefix Sum	Python
1011	Capacity To Ship Packages Within D Days	🟡 Medium	Array, Binary Search	Python
1042	Flower Planting With No Adjacent	🟡 Medium	Depth-First Search, Breadth-First Search, Graph Theory	Python
1047	Remove All Adjacent Duplicates In String	🟢 Easy	String, Stack	Python
1143	Longest Common Subsequence	🟡 Medium	String, Dynamic Programming	Python
1219	Path with Maximum Gold	🟡 Medium	Array, Backtracking, Matrix	Python
1386	Cinema Seat Allocation	🟡 Medium	Array, Hash Table, Greedy, Bit Manipulation	Python
1404	Number of Steps to Reduce a Number in Binary Representation to One	🟡 Medium	String, Bit Manipulation, Simulation	Python
1405	Longest Happy String	🟡 Medium	String, Greedy, Heap (Priority Queue)	Python
1443	Minimum Time to Collect All Apples in a Tree	🟡 Medium	Hash Table, Tree, Depth-First Search, Breadth-First Search	Python
1448	Count Good Nodes in Binary Tree	🟡 Medium	Tree, Depth-First Search, Breadth-First Search, Binary Tree	Python
1559	Detect Cycles in 2D Grid	🟡 Medium	Array, Depth-First Search, Breadth-First Search, Union-Find, Matrix	Python
2016	Maximum Difference Between Increasing Elements	🟢 Easy	Array	Python
2086	Minimum Number of Food Buckets to Feed the Hamsters	🟡 Medium	String, Dynamic Programming, Greedy	Python
2312	Selling Pieces of Wood	🔴 Hard	Array, Dynamic Programming, Memoization	Python
2384	Largest Palindromic Number	🟡 Medium	Hash Table, String, Greedy, Counting	Python
2385	Amount of Time for Binary Tree to Be Infected	🟡 Medium	Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree	Python
2850	Minimum Moves to Spread Stones Over Grid	🟡 Medium	Array, Dynamic Programming, Backtracking, Bit Manipulation, Matrix, Bitmask	Python
2906	Construct Product Matrix	🟡 Medium	Array, Matrix, Prefix Sum	Python
2909	Minimum Sum of Mountain Triplets II	🟡 Medium	Array, Prefix Sum	Python
3650	Minimum Cost Path with Edge Reversals	🟡 Medium	Graph Theory, Heap (Priority Queue), Shortest Path	Python

🏷️ By Topic

Array (63)

• 1. Two Sum
• 11. Container With Most Water
• 15. 3Sum
• 36. Valid Sudoku
• 39. Combination Sum
• 40. Combination Sum II
• 42. Trapping Rain Water
• 45. Jump Game II
• 48. Rotate Image
• 49. Group Anagrams
• 53. Maximum Subarray
• 55. Jump Game
• 56. Merge Intervals
• 57. Insert Interval
• 63. Unique Paths II
• 64. Minimum Path Sum
• 78. Subsets
• 79. Word Search
• 120. Triangle
• 121. Best Time to Buy and Sell Stock
• 122. Best Time to Buy and Sell Stock II
• 128. Longest Consecutive Sequence
• 130. Surrounded Regions
• 136. Single Number
• 139. Word Break
• 140. Word Break II
• 152. Maximum Product Subarray
• 153. Find Minimum in Rotated Sorted Array
• 162. Find Peak Element
• 167. Two Sum II - Input Array Is Sorted
• 198. House Robber
• 200. Number of Islands
• 213. House Robber II
• 238. Product of Array Except Self
• 309. Best Time to Buy and Sell Stock with Cooldown
• 322. Coin Change
• 329. Longest Increasing Path in a Matrix
• 332. Reconstruct Itinerary
• 347. Top K Frequent Elements
• 399. Evaluate Division
• 417. Pacific Atlantic Water Flow
• 498. Diagonal Traverse
• 560. Subarray Sum Equals K
• 621. Task Scheduler
• 622. Design Circular Queue
• 695. Max Area of Island
• 718. Maximum Length of Repeated Subarray
• 721. Accounts Merge
• 746. Min Cost Climbing Stairs
• 809. Expressive Words
• 875. Koko Eating Bananas
• 990. Satisfiability of Equality Equations
• 994. Rotting Oranges
• 1004. Max Consecutive Ones III
• 1011. Capacity To Ship Packages Within D Days
• 1219. Path with Maximum Gold
• 1386. Cinema Seat Allocation
• 1559. Detect Cycles in 2D Grid
• 2016. Maximum Difference Between Increasing Elements
• 2312. Selling Pieces of Wood
• 2850. Minimum Moves to Spread Stones Over Grid
• 2906. Construct Product Matrix
• 2909. Minimum Sum of Mountain Triplets II

Dynamic Programming (35)

• 5. Longest Palindromic Substring
• 22. Generate Parentheses
• 42. Trapping Rain Water
• 45. Jump Game II
• 53. Maximum Subarray
• 55. Jump Game
• 62. Unique Paths
• 63. Unique Paths II
• 64. Minimum Path Sum
• 70. Climbing Stairs
• 72. Edit Distance
• 91. Decode Ways
• 95. Unique Binary Search Trees II
• 96. Unique Binary Search Trees
• 97. Interleaving String
• 120. Triangle
• 121. Best Time to Buy and Sell Stock
• 122. Best Time to Buy and Sell Stock II
• 131. Palindrome Partitioning
• 139. Word Break
• 140. Word Break II
• 152. Maximum Product Subarray
• 198. House Robber
• 213. House Robber II
• 309. Best Time to Buy and Sell Stock with Cooldown
• 322. Coin Change
• 329. Longest Increasing Path in a Matrix
• 338. Counting Bits
• 718. Maximum Length of Repeated Subarray
• 746. Min Cost Climbing Stairs
• 787. Cheapest Flights Within K Stops
• 1143. Longest Common Subsequence
• 2086. Minimum Number of Food Buckets to Feed the Hamsters
• 2312. Selling Pieces of Wood
• 2850. Minimum Moves to Spread Stones Over Grid

Depth-First Search (31)

• 79. Word Search
• 98. Validate Binary Search Tree
• 130. Surrounded Regions
• 199. Binary Tree Right Side View
• 200. Number of Islands
• 207. Course Schedule
• 210. Course Schedule II
• 230. Kth Smallest Element in a BST
• 310. Minimum Height Trees
• 329. Longest Increasing Path in a Matrix
• 332. Reconstruct Itinerary
• 399. Evaluate Division
• 417. Pacific Atlantic Water Flow
• 547. Number of Provinces
• 684. Redundant Connection
• 695. Max Area of Island
• 721. Accounts Merge
• 743. Network Delay Time
• 785. Is Graph Bipartite?
• 787. Cheapest Flights Within K Stops
• 797. All Paths From Source to Target
• 802. Find Eventual Safe States
• 841. Keys and Rooms
• 863. All Nodes Distance K in Binary Tree
• 886. Possible Bipartition
• 947. Most Stones Removed with Same Row or Column
• 1042. Flower Planting With No Adjacent
• 1443. Minimum Time to Collect All Apples in a Tree
• 1448. Count Good Nodes in Binary Tree
• 1559. Detect Cycles in 2D Grid
• 2385. Amount of Time for Binary Tree to Be Infected

String (30)

• 3. Longest Substring Without Repeating Characters
• 5. Longest Palindromic Substring
• 12. Integer to Roman
• 13. Roman to Integer
• 20. Valid Parentheses
• 22. Generate Parentheses
• 49. Group Anagrams
• 71. Simplify Path
• 72. Edit Distance
• 79. Word Search
• 91. Decode Ways
• 97. Interleaving String
• 131. Palindrome Partitioning
• 139. Word Break
• 140. Word Break II
• 151. Reverse Words in a String
• 332. Reconstruct Itinerary
• 394. Decode String
• 399. Evaluate Division
• 424. Longest Repeating Character Replacement
• 468. Validate IP Address
• 721. Accounts Merge
• 809. Expressive Words
• 990. Satisfiability of Equality Equations
• 1047. Remove All Adjacent Duplicates In String
• 1143. Longest Common Subsequence
• 1404. Number of Steps to Reduce a Number in Binary Representation to One
• 1405. Longest Happy String
• 2086. Minimum Number of Food Buckets to Feed the Hamsters
• 2384. Largest Palindromic Number

Breadth-First Search (29)

• 102. Binary Tree Level Order Traversal
• 130. Surrounded Regions
• 199. Binary Tree Right Side View
• 200. Number of Islands
• 207. Course Schedule
• 210. Course Schedule II
• 310. Minimum Height Trees
• 322. Coin Change
• 329. Longest Increasing Path in a Matrix
• 399. Evaluate Division
• 417. Pacific Atlantic Water Flow
• 547. Number of Provinces
• 684. Redundant Connection
• 695. Max Area of Island
• 721. Accounts Merge
• 743. Network Delay Time
• 785. Is Graph Bipartite?
• 787. Cheapest Flights Within K Stops
• 797. All Paths From Source to Target
• 802. Find Eventual Safe States
• 841. Keys and Rooms
• 863. All Nodes Distance K in Binary Tree
• 886. Possible Bipartition
• 994. Rotting Oranges
• 1042. Flower Planting With No Adjacent
• 1443. Minimum Time to Collect All Apples in a Tree
• 1448. Count Good Nodes in Binary Tree
• 1559. Detect Cycles in 2D Grid
• 2385. Amount of Time for Binary Tree to Be Infected

Hash Table (24)

• 1. Two Sum
• 3. Longest Substring Without Repeating Characters
• 12. Integer to Roman
• 13. Roman to Integer
• 36. Valid Sudoku
• 49. Group Anagrams
• 128. Longest Consecutive Sequence
• 139. Word Break
• 140. Word Break II
• 146. LRU Cache
• 202. Happy Number
• 347. Top K Frequent Elements
• 355. Design Twitter
• 424. Longest Repeating Character Replacement
• 460. LFU Cache
• 560. Subarray Sum Equals K
• 621. Task Scheduler
• 721. Accounts Merge
• 863. All Nodes Distance K in Binary Tree
• 947. Most Stones Removed with Same Row or Column
• 1386. Cinema Seat Allocation
• 1443. Minimum Time to Collect All Apples in a Tree
• 2384. Largest Palindromic Number
• 2385. Amount of Time for Binary Tree to Be Infected

Graph Theory (19)

• 207. Course Schedule
• 210. Course Schedule II
• 310. Minimum Height Trees
• 329. Longest Increasing Path in a Matrix
• 332. Reconstruct Itinerary
• 399. Evaluate Division
• 547. Number of Provinces
• 684. Redundant Connection
• 743. Network Delay Time
• 785. Is Graph Bipartite?
• 787. Cheapest Flights Within K Stops
• 797. All Paths From Source to Target
• 802. Find Eventual Safe States
• 841. Keys and Rooms
• 886. Possible Bipartition
• 947. Most Stones Removed with Same Row or Column
• 990. Satisfiability of Equality Equations
• 1042. Flower Planting With No Adjacent
• 3650. Minimum Cost Path with Edge Reversals

Matrix (16)

• 36. Valid Sudoku
• 48. Rotate Image
• 63. Unique Paths II
• 64. Minimum Path Sum
• 79. Word Search
• 130. Surrounded Regions
• 200. Number of Islands
• 329. Longest Increasing Path in a Matrix
• 417. Pacific Atlantic Water Flow
• 498. Diagonal Traverse
• 695. Max Area of Island
• 994. Rotting Oranges
• 1219. Path with Maximum Gold
• 1559. Detect Cycles in 2D Grid
• 2850. Minimum Moves to Spread Stones Over Grid
• 2906. Construct Product Matrix

Union-Find (13)

• 128. Longest Consecutive Sequence
• 130. Surrounded Regions
• 200. Number of Islands
• 399. Evaluate Division
• 547. Number of Provinces
• 684. Redundant Connection
• 695. Max Area of Island
• 721. Accounts Merge
• 785. Is Graph Bipartite?
• 886. Possible Bipartition
• 947. Most Stones Removed with Same Row or Column
• 990. Satisfiability of Equality Equations
• 1559. Detect Cycles in 2D Grid

Backtracking (11)

• 22. Generate Parentheses
• 39. Combination Sum
• 40. Combination Sum II
• 78. Subsets
• 79. Word Search
• 95. Unique Binary Search Trees II
• 131. Palindrome Partitioning
• 140. Word Break II
• 797. All Paths From Source to Target
• 1219. Path with Maximum Gold
• 2850. Minimum Moves to Spread Stones Over Grid

Tree (10)

• 95. Unique Binary Search Trees II
• 96. Unique Binary Search Trees
• 98. Validate Binary Search Tree
• 102. Binary Tree Level Order Traversal
• 199. Binary Tree Right Side View
• 230. Kth Smallest Element in a BST
• 863. All Nodes Distance K in Binary Tree
• 1443. Minimum Time to Collect All Apples in a Tree
• 1448. Count Good Nodes in Binary Tree
• 2385. Amount of Time for Binary Tree to Be Infected

Binary Tree (9)

• 95. Unique Binary Search Trees II
• 96. Unique Binary Search Trees
• 98. Validate Binary Search Tree
• 102. Binary Tree Level Order Traversal
• 199. Binary Tree Right Side View
• 230. Kth Smallest Element in a BST
• 863. All Nodes Distance K in Binary Tree
• 1448. Count Good Nodes in Binary Tree
• 2385. Amount of Time for Binary Tree to Be Infected

Greedy (9)

• 11. Container With Most Water
• 45. Jump Game II
• 55. Jump Game
• 122. Best Time to Buy and Sell Stock II
• 621. Task Scheduler
• 1386. Cinema Seat Allocation
• 1405. Longest Happy String
• 2086. Minimum Number of Food Buckets to Feed the Hamsters
• 2384. Largest Palindromic Number

Heap (Priority Queue) (9)

• 295. Find Median from Data Stream
• 332. Reconstruct Itinerary
• 347. Top K Frequent Elements
• 355. Design Twitter
• 621. Task Scheduler
• 743. Network Delay Time
• 787. Cheapest Flights Within K Stops
• 1405. Longest Happy String
• 3650. Minimum Cost Path with Edge Reversals

Two Pointers (9)

• 5. Longest Palindromic Substring
• 11. Container With Most Water
• 15. 3Sum
• 42. Trapping Rain Water
• 151. Reverse Words in a String
• 167. Two Sum II - Input Array Is Sorted
• 202. Happy Number
• 295. Find Median from Data Stream
• 809. Expressive Words

Math (8)

• 2. Add Two Numbers
• 12. Integer to Roman
• 13. Roman to Integer
• 48. Rotate Image
• 62. Unique Paths
• 70. Climbing Stairs
• 96. Unique Binary Search Trees
• 202. Happy Number

Sorting (8)

• 15. 3Sum
• 49. Group Anagrams
• 56. Merge Intervals
• 295. Find Median from Data Stream
• 332. Reconstruct Itinerary
• 347. Top K Frequent Elements
• 621. Task Scheduler
• 721. Accounts Merge

Binary Search (7)

• 153. Find Minimum in Rotated Sorted Array
• 162. Find Peak Element
• 167. Two Sum II - Input Array Is Sorted
• 718. Maximum Length of Repeated Subarray
• 875. Koko Eating Bananas
• 1004. Max Consecutive Ones III
• 1011. Capacity To Ship Packages Within D Days

Bit Manipulation (7)

• 78. Subsets
• 136. Single Number
• 191. Number of 1 Bits
• 338. Counting Bits
• 1386. Cinema Seat Allocation
• 1404. Number of Steps to Reduce a Number in Binary Representation to One
• 2850. Minimum Moves to Spread Stones Over Grid

Design (5)

• 146. LRU Cache
• 295. Find Median from Data Stream
• 355. Design Twitter
• 460. LFU Cache
• 622. Design Circular Queue

Linked List (5)

• 2. Add Two Numbers
• 146. LRU Cache
• 355. Design Twitter
• 460. LFU Cache
• 622. Design Circular Queue

Memoization (5)

• 70. Climbing Stairs
• 139. Word Break
• 140. Word Break II
• 329. Longest Increasing Path in a Matrix
• 2312. Selling Pieces of Wood

Prefix Sum (5)

• 238. Product of Array Except Self
• 560. Subarray Sum Equals K
• 1004. Max Consecutive Ones III
• 2906. Construct Product Matrix
• 2909. Minimum Sum of Mountain Triplets II

Stack (5)

• 20. Valid Parentheses
• 42. Trapping Rain Water
• 71. Simplify Path
• 394. Decode String
• 1047. Remove All Adjacent Duplicates In String

Topological Sort (5)

• 207. Course Schedule
• 210. Course Schedule II
• 310. Minimum Height Trees
• 329. Longest Increasing Path in a Matrix
• 802. Find Eventual Safe States

Binary Search Tree (4)

• 95. Unique Binary Search Trees II
• 96. Unique Binary Search Trees
• 98. Validate Binary Search Tree
• 230. Kth Smallest Element in a BST

Shortest Path (4)

• 399. Evaluate Division
• 743. Network Delay Time
• 787. Cheapest Flights Within K Stops
• 3650. Minimum Cost Path with Edge Reversals

Sliding Window (4)

• 3. Longest Substring Without Repeating Characters
• 424. Longest Repeating Character Replacement
• 718. Maximum Length of Repeated Subarray
• 1004. Max Consecutive Ones III

Counting (3)

• 347. Top K Frequent Elements
• 621. Task Scheduler
• 2384. Largest Palindromic Number

Divide and Conquer (3)

• 53. Maximum Subarray
• 191. Number of 1 Bits
• 347. Top K Frequent Elements

Doubly-Linked List (2)

• 146. LRU Cache
• 460. LFU Cache

Recursion (2)

• 2. Add Two Numbers
• 394. Decode String

Simulation (2)

• 498. Diagonal Traverse
• 1404. Number of Steps to Reduce a Number in Binary Representation to One

Trie (2)

• 139. Word Break
• 140. Word Break II

Bitmask (1)

• 2850. Minimum Moves to Spread Stones Over Grid

Bucket Sort (1)

• 347. Top K Frequent Elements

Combinatorics (1)

• 62. Unique Paths

Data Stream (1)

• 295. Find Median from Data Stream

Eulerian Circuit (1)

• 332. Reconstruct Itinerary

Hash Function (1)

• 718. Maximum Length of Repeated Subarray

Monotonic Stack (1)

• 42. Trapping Rain Water

Queue (1)

• 622. Design Circular Queue

Quickselect (1)

• 347. Top K Frequent Elements

Rolling Hash (1)

• 718. Maximum Length of Repeated Subarray