🏆 Curated solutions to Leetcode problems in multiple languages to ace the Coding Interviews. #

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Array #

#	Solution	Tags	Difficulty	Remark
0001	Two Sum	Array, Hash Table
0004	Median of Two Sorted Arrays	Array, Binary Search, Divide & Conquer
0026	Remove Duplicates	Array, Two Pointers
0027	Remove Element	Array, Two Pointers
0035	Search Insert Position	Array, BS
0037	Sudoku Solver	Array, Backtracking, Matrix
0041	First Missing Positive	Array, Hash Table
0042	Trapping Rain Water	Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack
0048	Rotate Image	Array, Math, Matrix
0051	N-Queens	Array, Backtracking
0053	Maximum Subarray	Array, Divide and Conquer, DP
0055	Jump Game	Array, Dynamic Programming, Greedy
0066	Plus One	Array, Math
0074	Search a 2D Matrix	Array, Binary Search, Matrix
0075	Sort Colors	Array, Two Pointers, Sorting
0078	Subsets	Array, Backtracking, Bit Manip
0088	Merge Sorted Array	Array, Two Pointers, Sorting
0106	Construct Binary Tree from Inorder and Postorder Traversal	Array, Hash Table, Divide and Conquer, Tree, Binary Tree
0108	Convert Sorted Array to Binary Search Tree	Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0118	Pascal's Triangle	Array, DP
0119	Pascal's Triangle II	Array, DP
0121	Best Time to Buy and Sell Stock	Array, DP
0122	Best Time to Buy and Sell Stock II	Array, Dynamic Programming, Greedy
0136	Single Number	Array, Bit Manip
0169	Majority Element	Array, Hash Table, Divide and Conquer, Sorting, Counting
0200	Number of Islands	Array, Depth-First Search, Breadth-First Search, Union Find, Matrix
0217	Contains Duplicate	Array, Hash Table, Sorting
0219	Contains Duplicate II	Array, Hash Table, Sliding Window
0228	Summary Ranges	Array
0268	Missing Number	Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting
0283	Move Zeroes	Array, Two Pointers
0300	Longest Increasing Subsequence	Array, Binary Search, DP
0322	Coin Change	Array, Dynamic Programming, BFS
0349	Intersection of Two Arrays	Array, Hash Table, Two Pointers, Binary Search, Sorting
0350	Intersection of Two Arrays II	Array, Hash Table, Two Pointers, Binary Search, Sorting
0414	Third Maximum Number	Array, Sorting
0442	Find All Duplicates	Array, Hash Table
0448	Find All Numbers Disappeared in an Array	Array, Hash Table
0463	Island Perimeter	Array, Depth-First Search, Breadth-First Search, Matrix
0485	Max Consecutive Ones	Array
0498	Diagonal Traverse	Array, Matrix, Simulation
0502	IPO	Array, Greedy, Sorting, Heap (Priority Queue)
0506	Relative Ranks	Array, Sorting, Heap
0518	Coin Change 2	Array, DP
0540	Single Element in a Sorted Array	Array, BS
0605	Can Place Flowers	Array, Greedy
0695	Max Area of Island	Array, Depth-First Search, Breadth-First Search, Union Find, Matrix
0704	Binary Search	Array, Binary Search
0739	Daily Temperatures	Array, Stack, Monotonic Stack
0875	Koko Eating Bananas	Array, BS
0888	Fair Candy Swap	Array, Hash Table, Binary Search, Sorting
0912	Sort an Array	Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort
0944	Delete Columns to Make Sorted	Array, String
0997	Find the Town Judge	Array, Hash Table, Graph
1011	Capacity To Ship Packages Within D Days	Array, BS
1029	Two City Scheduling	Array, Greedy, Sorting
1232	Check If It Is a Straight Line	Array, Math, Geometry
1345	Jump Game IV	Array, Hash Table, Breadth-First Search
1431	Kids With the Greatest Number of Candies	Array
1472	Design Browser History	Array, Linked List, Stack, Design, Doubly-Linked List, Data Stream
1480	Running Sum of 1d Array	Array, Prefix Sum
1491	Average Salary Excluding the Minimum and Maximum	Array, Sorting
1498	Number of Subsequences That Satisfy the Given Sum Condition	Array, Two Pointers, Binary Search, Sorting
1512	Number of Good Pairs	Array, Hash Table, Math, Counting
1537	Get the Maximum Score	Array, Two Pointer, Dynamic Programming, Greedy
1539	Kth Missing Positive Number	Array, BS
1580	Shuffle the Array	Array
1672	Richest Customer Wealth	Array, Matrix
1920	Build Array from Permutation	Array, Simulation
1929	Concatenation of Array	Array
2011	Final Value of Variable After Performing Operations	Array, String, Simulation
2114	Maximum Number of Words Found in Sentences	Array, String
2176	Count Equal and Divisible Pairs in an Array	Array
2187	Minimum Time to Complete Trips	Array, BS
2348	Number of Zero-Filled Subarrays	Array, Math
2444	Count Subarrays With Fixed Bounds	Array, Queue, Sliding Window, Monotonic Queue
2551	Put Marbles in Bags	Array, Greedy, Sorting, Heap (Priority Queue)
2574	Left and Right Sum Differences	Array, Prefix Sum

String #

#	Solution	Tags	Difficulty	Remark
0013	Roman to Integer	String, Math, Hash Table
0014	Longest Common Prefix	String
0020	Valid Parentheses	String, ST
0022	Generate Parentheses	String, Dynamic Programming, Backtracking
0028	Find the Index of the First Occurrence in a String	Two Pointers, String, String Matching
0058	Length of Last Word	String
0067	Add Binary	Math, String, Bit Manipulation, Simulation
0072	Edit Distance	String, DP
0125	Valid Palindrome	Two Pointers, String
0205	Isomorphic Strings	Hash Table, String
0211	Design Add and Search Words Data Structure	String, Depth-First Search, Design, Trie
0242	Valid Anagram	Hash Table, String, Sorting
0257	Binary Tree Paths	String, Backtracking, Tree, Depth-First Search, Binary Tree
0290	Word Pattern	Hash Table, String
0344	Reverse String	Two Pointers, String, Recursion
0345	Reverse Vowels of a String	Two Pointers, String
0383	Ransom Note	Hash Table, String, Counting
0387	First Unique Character in a String	Hash Table, String, Queue, Counting
0389	Find the Difference	Hash Table, String, Bit Manipulation, Sorting
0392	Is Subsequence	Two Pointers, String, DP
0412	Fizz Buzz	Math, String, Simulation
0434	Number of Segments in a String	String
0438	Find All Anagrams in a String	Hash Table, String, Sliding Window
0443	String Compression	Two Pointers, String
0482	License Key Formatting	String
0516	Longest Palindromic Subsequence	String, DP
0541	Reverse String II	Two Pointers, String
0771	Jewels and Stones	String, Hashtable
0944	Delete Columns to Make Sorted	Array, String
1047	Remove All Adjacent Duplicates In String	String, Stack
1092	Shortest Common Supersequence	String, DP
1108	Defanging an IP Address	String
1143	Longest Common Subsequence	String, DP
1461	Check If a String Contains All Binary Codes of Size K	String, Hash Table, Bit Manipulation
1689	Partitioning Into Minimum Number Of Deci-Binary Numbers	String, Greedy
1957	Delete Characters to Make Fancy String	String
2011	Final Value of Variable After Performing Operations	Array, String, Simulation
2114	Maximum Number of Words Found in Sentences	Array, String

Hash Table #

#	Solution	Tags	Difficulty	Remark
0001	Two Sum	Array, Hash Table
0013	Roman to Integer	String, Math, Hash Table
0041	First Missing Positive	Array, Hash Table
0106	Construct Binary Tree from Inorder and Postorder Traversal	Array, Hash Table, Divide and Conquer, Tree, Binary Tree
0141	Linked List Cycle	Hash Table, Linked List, 2P
0142	Linked List Cycle II	Hash Table, Linked List, 2P
0160	Intersection of Two Linked Lists	Hash Table, Linked List, 2P
0169	Majority Element	Array, Hash Table, Divide and Conquer, Sorting, Counting
0202	Happy Number	Hash Table, Math, 2P
0205	Isomorphic Strings	Hash Table, String
0217	Contains Duplicate	Array, Hash Table, Sorting
0219	Contains Duplicate II	Array, Hash Table, Sliding Window
0242	Valid Anagram	Hash Table, String, Sorting
0268	Missing Number	Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting
0290	Word Pattern	Hash Table, String
0349	Intersection of Two Arrays	Array, Hash Table, Two Pointers, Binary Search, Sorting
0350	Intersection of Two Arrays II	Array, Hash Table, Two Pointers, Binary Search, Sorting
0383	Ransom Note	Hash Table, String, Counting
0387	First Unique Character in a String	Hash Table, String, Queue, Counting
0389	Find the Difference	Hash Table, String, Bit Manipulation, Sorting
0438	Find All Anagrams in a String	Hash Table, String, Sliding Window
0442	Find All Duplicates	Array, Hash Table
0448	Find All Numbers Disappeared in an Array	Array, Hash Table
0652	Find Duplicate Subtrees	Hash Table, Tree, Depth-First Search, Binary Tree
0653	Two Sum IV - Input is a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0888	Fair Candy Swap	Array, Hash Table, Binary Search, Sorting
0771	Jewels and Stones	String, Hashtable
0997	Find the Town Judge	Array, Hash Table, Graph
1345	Jump Game IV	Array, Hash Table, Breadth-First Search
1512	Number of Good Pairs	Array, Hash Table, Math, Counting

Dynamic Programming #

#	Solution	Tags	Difficulty	Remark
0022	Generate Parentheses	String, Dynamic Programming, Backtracking
0042	Trapping Rain Water	Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack
0053	Maximum Subarray	Array, Divide and Conquer, DP
0055	Jump Game	Array, Dynamic Programming, Greedy
0070	Climbing Stairs	Math, Dynamic Programming, Memoization
0072	Edit Distance	String, DP
0118	Pascal's Triangle	Array, DP
0119	Pascal's Triangle II	Array, DP
0121	Best Time to Buy and Sell Stock	Array, DP
0122	Best Time to Buy and Sell Stock II	Array, Dynamic Programming, Greedy
0279	Perfect Squares	Math, Dynamic Programming, Breadth-First Search
0300	Longest Increasing Subsequence	Array, Binary Search, DP
0322	Coin Change	Array, Dynamic Programming, BFS
0337	House Robber III	Dynamic Programming, Tree, Depth First Search, Binary Tree
0338	Counting Bits	Dynamic Programming, Bit Manip
0392	Is Subsequence	Two Pointers, String, DP
0509	Fibonacci Number	Math, Recursion, Dynamic Programming, Memoization
0516	Longest Palindromic Subsequence	String, DP
0518	Coin Change 2	Array, DP
1092	Shortest Common Supersequence	String, DP
1143	Longest Common Subsequence	String, DP
1537	Get the Maximum Score	Array, Two Pointer, Dynamic Programming, Greedy

Math #

#	Solution	Tags	Difficulty	Remark
0002	Add Two Numbers	Linked List, Math, Recursion
0007	Reverse Integer	Math
0009	Palindrome Number	Math
0013	Roman to Integer	String, Math, Hash Table
0048	Rotate Image	Array, Math, Matrix
0066	Plus One	Array, Math
0067	Add Binary	Math, String, Bit Manipulation, Simulation
0069	Sqrt(x)	Math, BS
0070	Climbing Stairs	Math, Dynamic Programming, Memorization
0172	Factorial Trailiing Zeroes	Math
0202	Happy Number	Hash Table, Math, 2P
0231	Power of Two	Math, Bit Manipulation, Recursion
0258	Add Digits	Math, Simulation, Number Theory
0263	Ugly Number	Math
0268	Missing Number	Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting
0279	Perfect Squares	Math, Dynamic Programming, Breadth-First Search
0292	Nim Game	Math, Brainteaser, Game Theory
0326	Power of Three	Math, Recursion
0342	Power of Four	Math, Bit Manipulation, Recursion
0367	Valid Perfect Square	Math, Binary Search
0382	Linked List Random Node	Linked List, Math, Reservoir Sampling, Randomized
0412	Fizz Buzz	Math, String, Simulation
0441	Arranging Coins	Math, BS
0445	Add Two Numbers II	Linked List, Math, Stack
0492	Construct the Rectangle	Math
0504	Base 7	Math
0507	Perfect Number	Math
0509	Fibonacci Number	Math, Recursion, Dynamic Programming, Memoization
1232	Check If It Is a Straight Line	Array, Math, Geometry
1512	Number of Good Pairs	Array, Hash Table, Math, Counting
1630	Count Odd Numbers in an Interval Range	Math
2160	Minimum Sum of Four Digit Number After Splitting Digits	Math, Greedy, Sorting
2235	Add Two Integers	Math
2348	Number of Zero-Filled Subarrays	Array, Math
2396	Strictly Palindromic Number	Math, Two Pointers, Brainteaser
2413	Smallest Even Multiple	Math, Number Theory
2427	Number of Common Factors	Math, Enumeration, Number Theory
2469	Convert the Temperature	Math

Sorting #

#	Solution	Tags	Difficulty	Remark
0075	Sort Colors	Array, Two Pointers, Sorting
0088	Merge Sorted Array	Array, Two Pointers, Sorting
0169	Majority Element	Array, Hash Table, Divide and Conquer, Sorting, Counting
0217	Contains Duplicate	Array, Hash Table, Sorting
0242	Valid Anagram	Hash Table, String, Sorting
0268	Missing Number	Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting
0349	Intersection of Two Arrays	Array, Hash Table, Two Pointers, Binary Search, Sorting
0350	Intersection of Two Arrays II	Array, Hash Table, Two Pointers, Binary Search, Sorting
0389	Find the Difference	Hash Table, String, Bit Manipulation, Sorting
0414	Third Maximum Number	Array, Sorting
0502	IPO	Array, Greedy, Sorting, Heap (Priority Queue)
0506	Relative Ranks	Array, Sorting, Heap
0888	Fair Candy Swap	Array, Hash Table, Binary Search, Sorting
0912	Sort an Array	Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort
1029	Two City Scheduling	Array, Greedy, Sorting
1498	Number of Subsequences That Satisfy the Given Sum Condition	Array, Two Pointers, Binary Search, Sorting
1491	Average Salary Excluding the Minimum and Maximum	Array, Sorting
2160	Minimum Sum of Four Digit Number After Splitting Digits	Math, Greedy, Sorting
2551	Put Marbles in Bags	Array, Greedy, Sorting, Heap (Priority Queue)

Depth First Search #

#	Solution	Tags	Difficulty	Remark
0100	Same Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0104	Maximum Depth of Binary Tree	Tree, Breadth First Search, Depth First Search, Binary Tree
0110	Balanced Binary Tree	Tree, Depth First Search, Binary Tree
0111	Minimum Depth of Binary Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0144	Binary Tree Preorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0145	Binary Tree Postorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0199	Binary Tree Right Side View	Tree, Depth First Search, Breadth First Search, Binary Tree
0222	Count Complete Tree Nodes	Binary Search, Tree, Depth First Search, Binary Tree
0230	Kth Smallest Element in a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0337	House Robber III	Dynamic Programming, Tree, Depth First Search, Binary Tree
0543	Diameter of Binary Tree	Tree, Depth First Search, Binary Tree
0653	Two Sum IV - Input is a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree

Greedy #

#	Solution	Tags	Difficulty	Remark
0055	Jump Game	Array, Dynamic Programming, Greedy
0094	Binary Tree Inorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0098	Validate Binary Search Tree	Tree, Depth First Search, Binary Search Tree, Binary Tree
0122	Best Time to Buy and Sell Stock II	Array, Dynamic Programming, Greedy
0502	IPO	Array, Greedy, Sorting, Heap (Priority Queue)
0605	Can Place Flowers	Array, Greedy
1029	Two City Scheduling	Array, Greedy, Sorting
1537	Get the Maximum Score	Array, Two Pointer, Dynamic Programming, Greedy
1689	Partitioning Into Minimum Number Of Deci-Binary Numbers	String, Greedy
2160	Minimum Sum of Four Digit Number After Splitting Digits	Math, Greedy, Sorting
2551	Put Marbles in Bags	Array, Greedy, Sorting, Heap (Priority Queue)

Database #

Breadth First Search #

#	Solution	Tags	Difficulty	Remark
0100	Same Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0103	Binary Tree Zigzag Level Order Traversal	Tree, Breadth First Search, Binary Tree
0104	Maximum Depth of Binary Tree	Tree, Breadth First Search, Depth First Search, Binary Tree
0111	Minimum Depth of Binary Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0199	Binary Tree Right Side View	Tree, Depth First Search, Breadth First Search, Binary Tree
0230	Kth Smallest Element in a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0322	Coin Change	Array, Dynamic Programming, BFS
0653	Two Sum IV - Input is a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree

Tree #

#	Solution	Tags	Difficulty	Remark
0094	Binary Tree Inorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0098	Validate Binary Search Tree	Tree, Depth First Search, Binary Search Tree, Binary Tree
0100	Same Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0101	Symmetric Tree	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0103	Binary Tree Zigzag Level Order Traversal	Tree, Breadth First Search, Binary Tree
0104	Maximum Depth of Binary Tree	Tree, Breadth First Search, Depth First Search, Binary Tree
0106	Construct Binary Tree from Inorder and Postorder Traversal	Array, Hash Table, Divide and Conquer, Tree, Binary Tree
0108	Convert Sorted Array to Binary Search Tree	Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0109	Convert Sorted List to Binary Search Tree	Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0110	Balanced Binary Tree	Tree, Depth First Search, Binary Tree
0111	Minimum Depth of Binary Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0112	Path Sum	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0129	Sum Root to Leaf Numbers	Tree, Depth-First Search, Binary Tree
0144	Binary Tree Preorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0145	Binary Tree Postorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0199	Binary Tree Right Side View	Tree, Depth First Search, Breadth First Search, Binary Tree
0222	Count Complete Tree Nodes	Binary Search, Tree, Depth First Search, Binary Tree
0226	Invert Binary Tree	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0230	Kth Smallest Element in a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0236	Lowest Common Ancestor of a Binary Tree	Tree, Depth-First Search, Binary Tree
0257	Binary Tree Paths	String, Backtracking, Tree, Depth-First Search, Binary Tree
0337	House Robber III	Dynamic Programming, Tree, Depth First Search, Binary Tree
0404	Sum of Left Leaves	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0530	Minimum Absolute Difference in BST	Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree
0543	Diameter of Binary Tree	Tree, Depth First Search, Binary Tree
0652	Find Duplicate Subtrees	Hash Table, Tree, Depth-First Search, Binary Tree
0653	Two Sum IV - Input is a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0799	Minimum Distance Between BST Nodes	Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree
0958	Check Completeness of a Binary Tree	Tree, Breadth-First Search, Binary Tree
2236	Root Equal to Sum of Children	Tree, Binary Tree

Binary Search #

#	Solution	Tags	Difficulty	Remark
0004	Median of Two Sorted Arrays	Array, Binary Search, Divide & Conquer
0035	Search Insert Position	Array, BS
0069	Sqrt(x)	Math, BS
0074	Search a 2D Matrix	Array, Binary Search, Matrix
0222	Count Complete Tree Nodes	Binary Search, Tree, Depth First Search, Binary Tree
0268	Missing Number	Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting
0278	First Bad Version	Binary Search, Interactive
0300	Longest Increasing Subsequence	Array, Binary Search, DP
0349	Intersection of Two Arrays	Array, Hash Table, Two Pointers, Binary Search, Sorting
0350	Intersection of Two Arrays II	Array, Hash Table, Two Pointers, Binary Search, Sorting
0367	Valid Perfect Square	Math, Binary Search
0374	Guess Number Higher or Lower	Binary Search, Interactive
0441	Arranging Coins	Math, BS
0540	Single Element in a Sorted Array	Array, BS
0704	Binary Search	Array, Binary Search
0875	Koko Eating Bananas	Array, BS
1011	Capacity To Ship Packages Within D Days	Array, BS
1498	Number of Subsequences That Satisfy the Given Sum Condition	Array, Two Pointers, Binary Search, Sorting
0888	Fair Candy Swap	Array, Hash Table, Binary Search, Sorting
1539	Kth Missing Positive Number	Array, BS
2187	Minimum Time to Complete Trips	Array, BS

Matrix #

#	Solution	Tags	Difficulty	Remark
0037	Sudoku Solver	Array, Backtracking, Matrix
0048	Rotate Image	Array, Math, Matrix
0074	Search a 2D Matrix	Array, Binary Search, Matrix
0200	Number of Islands	Array, Depth-First Search, Breadth-First Search, Union Find, Matrix
0463	Island Perimeter	Array, Depth-First Search, Breadth-First Search, Matrix
0498	Diagonal Traverse	Array, Matrix, Simulation
0695	Max Area of Island	Array, Depth-First Search, Breadth-First Search, Union Find, Matrix
1672	Richest Customer Wealth	Array, Matrix

Binary Tree #

#	Solution	Tags	Difficulty	Remark
0094	Binary Tree Inorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0098	Validate Binary Search Tree	Tree, Depth First Search, Binary Search Tree, Binary Tree
0100	Same Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0101	Symmetric Tree	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0103	Binary Tree Zigzag Level Order Traversal	Tree, Breadth First Search, Binary Tree
0104	Maximum Depth of Binary Tree	Tree, Breadth First Search, Depth First Search, Binary Tree
0106	Construct Binary Tree from Inorder and Postorder Traversal	Array, Hash Table, Divide and Conquer, Tree, Binary Tree
0108	Convert Sorted Array to Binary Search Tree	Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0109	Convert Sorted List to Binary Search Tree	Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0110	Balanced Binary Tree	Tree, Depth First Search, Binary Tree
0111	Minimum Depth of Binary Tree	Tree, Depth First Search, Breadth First Search, Binary Tree
0112	Path Sum	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0129	Sum Root to Leaf Numbers	Tree, Depth-First Search, Binary Tree
0144	Binary Tree Preorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0145	Binary Tree Postorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0199	Binary Tree Right Side View	Tree, Depth First Search, Breadth First Search, Binary Tree
0222	Count Complete Tree Nodes	Binary Search, Tree, Depth First Search, Binary Tree
0226	Invert Binary Tree	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0230	Kth Smallest Element in a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0236	Lowest Common Ancestor of a Binary Tree	Tree, Depth-First Search, Binary Tree
0257	Binary Tree Paths	String, Backtracking, Tree, Depth-First Search, Binary Tree
0337	House Robber III	Dynamic Programming, Tree, Depth First Search, Binary Tree
0404	Sum of Left Leaves	Tree, Depth-First Search, Breadth-First Search, Binary Tree
0530	Minimum Absolute Difference in BST	Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree
0543	Diameter of Binary Tree	Tree, Depth First Search, Binary Tree
0652	Find Duplicate Subtrees	Hash Table, Tree, Depth-First Search, Binary Tree
0653	Two Sum IV - Input is a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0799	Minimum Distance Between BST Nodes	Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree
0958	Check Completeness of a Binary Tree	Tree, Breadth-First Search, Binary Tree
2236	Root Equal to Sum of Children	Tree, Binary Tree

Two Pointers #

#	Solution	Tags	Difficulty	Remark
0004	Median of Two Sorted Arrays	Array, Binary Search, Divide & Conquer
0027	Remove Element	Array, Two Pointers
0028	Find the Index of the First Occurrence in a String	Two Pointers, String, String Matching
0042	Trapping Rain Water	Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack
0061	Rotate List	Linked List, Two Pointers
0075	Sort Colors	Array, Two Pointers, Sorting
0088	Merge Sorted Array	Array, Two Pointers, Sorting
0125	Valid Palindrome	Two Pointers, String
0141	Linked List Cycle	Hash Table, Linked List, 2P
0142	Linked List Cycle II	Hash Table, Linked List, 2P
0160	Intersection of Two Linked Lists	Hash Table, Linked List, 2P
0202	Happy Number	Hash Table, Math, 2P
0234	Palindrome Linked List	Linked List, Two Pointers, Stack, Recursion
0283	Move Zeroes	Array, Two Pointers
0344	Reverse String	Two Pointers, String, Recursion
0345	Reverse Vowels of a String	Two Pointers, String
0349	Intersection of Two Arrays	Array, Hash Table, Two Pointers, Binary Search, Sorting
0350	Intersection of Two Arrays II	Array, Hash Table, Two Pointers, Binary Search, Sorting
0392	Is Subsequence	Two Pointers, String, DP
0443	String Compression	Two Pointers, String
0541	Reverse String II	Two Pointers, String
0653	Two Sum IV - Input is a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0876	Middle of the Linked List	Linked List, Two Pointers
1498	Number of Subsequences That Satisfy the Given Sum Condition	Array, Two Pointers, Binary Search, Sorting
1537	Get the Maximum Score	Array, Two Pointer, Dynamic Programming, Greedy
2396	Strictly Palindromic Number	Math, Two Pointers, Brainteaser

Bit Manipulation #

#	Solution	Tags	Difficulty	Remark
0067	Add Binary	Math, String, Bit Manipulation, Simulation
0078	Subsets	Array, Backtracking, Bit Manip
0136	Single Number	Array, Bit Manip
0190	Reverse Bits	Divide and Conquer, Bit Manip
0191	Number of 1 Bits	Divide & Conquer, Bit Manipulation
0231	Power of Two	Math, Bit Manipulation, Recursion
0268	Missing Number	Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting
0338	Counting Bits	Dynamic Programming, Bit Manip
0342	Power of Four	Math, Bit Manipulation, Recursion
0389	Find the Difference	Hash Table, String, Bit Manipulation, Sorting
0401	Binary Watch	Backtracking, Bit Manip
0461	Hamming Distance	Bit Manip
0476	Number Complement	Bit Manip
1461	Check If a String Contains All Binary Codes of Size K	String, Hash Table, Bit Manipulation

Stack #

#	Solution	Tags	Difficulty	Remark
0020	Valid Parentheses	String, ST
0042	Trapping Rain Water	Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack
0094	Binary Tree Inorder Traversal	Tree, Stack, Depth First Search, Binary Tree
0144	Binary Tree Preorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0145	Binary Tree Postorder Traversal	Stack, Tree, Depth First Search, Binary Tree
0225	Implement Stack using Queues	Stack, Design, Q
0232	Implement Queue using Stacks	Stack, Design, Q
0234	Palindrome Linked List	Linked List, Two Pointers, Stack, Recursion
0445	Add Two Numbers II	Linked List, Math, Stack
0739	Daily Temperatures	Array, Stack, Monotonic Stack
1047	Remove All Adjacent Duplicates In String	String, Stack
1472	Design Browser History	Array, Linked List, Stack, Design, Doubly-Linked List, Data Stream

Design #

#	Solution	Tags	Difficulty	Remark
0211	Design Add and Search Words Data Structure	String, Depth-First Search, Design, Trie
0225	Implement Stack using Queues	Stack, Design, Q
0232	Implement Queue using Stacks	Stack, Design, Q
1472	Design Browser History	Array, Linked List, Stack, Design, Doubly-Linked List, Data Stream

Heap (Priority Queue) #

#	Solution	Tags	Difficulty	Remark
0506	Relative Ranks	Array, Sorting, Heap

Graph #

#	Solution	Tags	Difficulty	Remark
0997	Find the Town Judge	Array, Hash Table, Graph

Simulation #

#	Solution	Tags	Difficulty	Remark
0067	Add Binary	Math, String, Bit Manipulation, Simulation
0258	Add Digits	Math, Simulation, Number Theory
0412	Fizz Buzz	Math, String, Simulation
0498	Diagonal Traverse	Array, Matrix, Simulation
1920	Build Array from Permutation	Array, Simulation
2011	Final Value of Variable After Performing Operations	Array, String, Simulation

Backtracking #

#	Solution	Tags	Difficulty	Remark
0022	Generate Parentheses	String, Dynamic Programming, Backtracking
0037	Sudoku Solver	Array, Backtracking, Matrix
0051	N-Queens	Array, Backtracking
0078	Subsets	Array, Backtracking, Bit Manip
0257	Binary Tree Paths	String, Backtracking, Tree, Depth-First Search, Binary Tree
0401	Binary Watch	Backtracking, Bit Manip

Prefix Sum #

#	Solution	Tags	Difficulty	Remark
1480	Running Sum of 1d Array	Array, Prefix Sum
2574	Left and Right Sum Differences	Array, Prefix Sum

Counting #

#	Solution	Tags	Difficulty	Remark
0169	Majority Element	Array, Hash Table, Divide and Conquer, Sorting, Counting
0383	Ransom Note	Hash Table, String, Counting
0387	First Unique Character in a String	Hash Table, String, Queue, Counting
1512	Number of Good Pairs	Array, Hash Table, Math, Counting

Sliding Window #

#	Solution	Tags	Difficulty	Remark
0219	Contains Duplicate II	Array, Hash Table, Sliding Window
0438	Find All Anagrams in a String	Hash Table, String, Sliding Window
2444	Count Subarrays With Fixed Bounds	Array, Queue, Sliding Window, Monotonic Queue

Linked List #

#	Solution	Tags	Difficulty	Remark
0002	Add Two Numbers	Linked List, Math, Recursion
0021	Merge Two Sorted Lists	Linked List, Recursion
0024	Swap Nodes in Pairs	Linked List, Recursion
0061	Rotate List	Linked List, Two Pointers
0083	Remove Duplicates from Sorted List	LL
0109	Convert Sorted List to Binary Search Tree	Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0141	Linked List Cycle	Hash Table, Linked List, 2P
0142	Linked List Cycle II	Hash Table, Linked List, 2P
0160	Intersection of Two Linked Lists	Hash Table, Linked List, 2P
0203	Remove Linked List Elements	Linked List, Recursion
0206	Reverse Linked List	Linked List, Recursion
0234	Palindrome Linked List	Linked List, Two Pointers, Stack, Recursion
0369	Plus One Linked List	Linked List, Math		🔒
0382	Linked List Random Node	Linked List, Math, Reservoir Sampling, Randomized
0445	Add Two Numbers II	Linked List, Math, Stack
0876	Middle of the Linked List	Linked List, Two Pointers
1472	Design Browser History	Array, Linked List, Stack, Design, Doubly-Linked List, Data Stream

Union Find #

#	Solution	Tags	Difficulty	Remark
0200	Number of Islands	Array, Depth-First Search, Breadth-First Search, Union Find, Matrix
0695	Max Area of Island	Array, Depth-First Search, Breadth-First Search, Union Find, Matrix

Ordered Set #

Monotonic Stack #

#	Solution	Tags	Difficulty	Remark
0042	Trapping Rain Water	Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack
0739	Daily Temperatures	Array, Stack, Monotonic Stack

Recursion #

#	Solution	Tags	Difficulty	Remark
0002	Add Two Numbers	Linked List, Math, Recursion
0021	Merge Two Sorted Lists	Linked List, Recursion
0024	Swap Nodes in Pairs	Linked List, Recursion
0203	Remove Linked List Elements	Linked List, Recursion
0206	Reverse Linked List	Linked List, Recursion
0231	Power of Two	Math, Bit Manipulation, Recursion
0234	Palindrome Linked List	Linked List, Two Pointers, Stack, Recursion
0326	Power of Three	Math, Recursion
0342	Power of Four	Math, Bit Manipulation, Recursion
0344	Reverse String	Two Pointers, String, Recursion
0509	Fibonacci Number	Math, Recursion, Dynamic Programming, Memoization

Trie #

#	Solution	Tags	Difficulty	Remark
0211	Design Add and Search Words Data Structure	String, Depth-First Search, Design, Trie

Binary Search Tree #

#	Solution	Tags	Difficulty	Remark
0108	Convert Sorted Array to Binary Search Tree	Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0109	Convert Sorted List to Binary Search Tree	Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0530	Minimum Absolute Difference in BST	Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree
0653	Two Sum IV - Input is a BST	Tree, Depth First Search, Binary Search Tree, Binary Tree
0799	Minimum Distance Between BST Nodes	Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree

Divide and Conquer #

#	Solution	Tags	Difficulty	Remark
0004	Median of Two Sorted Arrays	Array, Binary Search, Divide & Conquer
0053	Maximum Subarray	Array, Divide and Conquer, DP
0106	Construct Binary Tree from Inorder and Postorder Traversal	Array, Hash Table, Divide and Conquer, Tree, Binary Tree
0108	Convert Sorted Array to Binary Search Tree	Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0109	Convert Sorted List to Binary Search Tree	Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree
0169	Majority Element	Array, Hash Table, Divide and Conquer, Sorting, Counting
0190	Reverse Bits	Divide and Conquer, Bit Manip
0191	Number of 1 Bits	Divide & Conquer, Bit Manipulation
0912	Sort an Array	Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort

Enumeration #

#	Solution	Tags	Difficulty	Remark
2427	Number of Common Factors	Math, Enumeration, Number Theory

Bitmask #

Queue #

#	Solution	Tags	Difficulty	Remark
0225	Implement Stack using Queues	Stack, Design, Q
0232	Implement Queue using Stacks	Stack, Design, Q
0387	First Unique Character in a String	Hash Table, String, Queue, Counting
2444	Count Subarrays With Fixed Bounds	Array, Queue, Sliding Window, Monotonic Queue

Memoization #

#	Solution	Tags	Difficulty	Remark
0070	Climbing Stairs	Math, Dynamic Programming, Memoization
0509	Fibonacci Number	Math, Recursion, Dynamic Programming, Memoization

Geometry #

#	Solution	Tags	Difficulty	Remark
1232	Check If It Is a Straight Line	Array, Math, Geometry

Topological Sort #

Segment Tree #

Game Theory #

#	Solution	Tags	Difficulty	Remark
0292	Nim Game	Math, Brainteaser, Game Theory

Hash Function #

#	Solution	Tags	Difficulty	Remark
1461	Check If a String Contains All Binary Codes of Size K	String, Hash Table, Rolling Hash, Hash Function

Binary Indexed Tree #

Interactive #

#	Solution	Tags	Difficulty	Remark
0278	First Bad Version	Binary Search, Interactive
0374	Guess Number Higher or Lower	Binary Search, Interactive

String Matching #

#	Solution	Tags	Difficulty	Remark
0028	Find the Index of the First Occurrence in a String	Two Pointers, String, String Matching

Rolling Hash #

#	Solution	Tags	Difficulty	Remark
1461	Check If a String Contains All Binary Codes of Size K	String, Hash Table, Rolling Hash, Hash Function

Shortest Path #

Number Theory #

#	Solution	Tags	Difficulty	Remark
0258	Add Digits	Math, Simulation, Number Theory
2413	Smallest Even Multiple	Math, Number Theory
2427	Number of Common Factors	Math, Enumeration, Number Theory

Data Stream #

#	Solution	Tags	Difficulty	Remark
1472	Design Browser History	Array, Linked List, Stack, Design, Doubly-Linked List, Data Stream

Combinatorics #

Randomized #

#	Solution	Tags	Difficulty	Remark
0382	Linked List Random Node	Linked List, Math, Reservoir Sampling, Randomized

Monotonic Queue #

#	Solution	Tags	Difficulty	Remark
2444	Count Subarrays With Fixed Bounds	Array, Queue, Sliding Window, Monotonic Queue

Iterator #

Merge Sort #

#	Solution	Tags	Difficulty	Remark
0912	Sort an Array	Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort

Concurrency #

Doubly Linked List #

Brainteaser #

#	Solution	Tags	Difficulty	Remark
0292	Nim Game	Math, Brainteaser, Game Theory
2396	Strictly Palindromic Number	Math, Two Pointers, Brainteaser

Probability and Statistics #

Quickselect #

Bucket Sort #

#	Solution	Tags	Difficulty	Remark
0912	Sort an Array	Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort

Suffix Array #

Minimum Spanning Tree #

Counting Sort #

#	Solution	Tags	Difficulty	Remark
0912	Sort an Array	Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort

Shell #

#	Solution	Tags	Difficulty	Remark
0193	Valid Phone Numbers	Shell
0195	Tenth Line	Shell

Line Sweep #

Reservoir Sampling #

#	Solution	Tags	Difficulty	Remark
0382	Linked List Random Node	Linked List, Math, Reservoir Sampling, Randomized

Eulerian Circuit #

Radix Sort #

#	Solution	Tags	Difficulty	Remark
0912	Sort an Array	Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort

Strongly Connected Component #

Rejection Sampling #

Biconnected Component #