Content

By data structure

• Bit, String and Integer
• Array
• Stack and Queue
• Hash Table
• Linked list
• Heap
• Tree

By paradigm and implementation

• Search
• Sort
• Greedy
• Divide and Conquer
• Recursion
• Dynamic Programming
• Backtracking
• Two Pointers and Sliding Windows

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By data structure

Bit, String and Integer

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0009	Palindrome Number	Python	Easy 🥉	Integer
0014	Longest Common Prefix	Python	Easy 🥉	String
0020	Valid Parentheses	Python	Easy 🥉	String, Stack
0067	Add Binary 🔒	Python	Easy 🥉	Binary Number, String
0136	Single Number	Python	Easy 🥉	Hash Table	Bit Manipulation
0190	Reverse Bits	Python	Easy 🥉	Binary Number	Bit Manipulation
0204	Count Primes	Python	Easy 🥉
0070	Climbing Stairs	Python	Easy 🥉	Integer	Recursion, Dynamic Programming
0268	Missing Number	Python	Easy 🥉	Array, Hash Table	Sort, Bit Manipulation
0387	First Unique Character in a String	Python	Easy 🥉	String, Hash Table
0392	Is Subsequence 🔒	Python	Easy 🥉	String	Two Pointers, Greedy, Recursion, Dynamic Programming, Binary Search
0929	Unique Email Addresses	Python	Easy 🥉	String
1022	Sum of Root To Leaf Binary Numbers	Python	Easy 🥉	Tree	Recursion, DFS, BFS, Bit Manipulation
1290	Convert Binary Number in a Linked List to Integer	Python	Easy 🥉	Linked Lists	Recursion, Bit Manipulation
0003	Longest Substring Without Repeating Characters 🔒	Python	Medium 🥈	String, Hash Table	Sliding Windows
0005	Longest Palindromic Substring	Python	Medium 🥈	String	Dynamic Programming
0022	Generate Parentheses	Python	Medium 🥈	String	Recursion, Dynamic Programming
0078	Subsets	Python	Medium 🥈	Array	Backtracking, Bit Manipulation
0338	Counting Bits🔒	Python	Medium 🥈	Binary Number	Bit Manipulation, Dynamic Programming

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Array

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0001	Two Sum	Python	Easy 🥉	Array, Hash Table
0035	Search Insert Position 🔒	Python	Easy 🥉	Array	Binary Search
0053	Maximum Subarray 🔒	Python	Easy 🥉	Array	Dynamic Programming, Divide and Conquer, Recursion
0118	Pascal's Triangle	Python	Easy 🥉	Array	Recursion, Dynamic Programming
0121	Best Time to Buy and Sell Stock	Python	Easy 🥉	Array	Dynamic Programming
0122	Best Time to Buy and Sell Stock II	Python	Easy 🥉	Array	Greedy
0169	Majority Element	Python	Easy 🥉	Array, Hash Table	Sort
0171	Excel Sheet Column Number 🔒	Python	Easy 🥉	Array
0217	Contains Duplicate	Python	Easy 🥉	Array, Hash Table	Sort
0242	Valid Anagram	Python	Easy 🥉	Array, Hash Table	Sort
0268	Missing Number	Python	Easy 🥉	Array, Hash Table	Sort, Bit Manipulation
0283	Move Zeroes	Python	Easy 🥉	Array	Two Pointers
0344	Reverse String	Python	Easy 🥉	Array	Two Pointers
0349	Intersection of Two Arrays	Python	Easy 🥉	Array, Hash Table	Sort, Binary Search, Two Pointers
0350	Intersection of Two Arrays II 🔒	Python	Easy 🥉	Array, Hash Table	Sort, Two Pointers
0448	Find All Numbers Disappeared in an Array 🔒	Python	Easy 🥉	Array, Hash Table
0463	Island Perimeter 🔒	Python	Easy 🥉	Array
0704	Binary Search	Python	Easy 🥉	Array	Binary Search, Recursion
0746	Min Cost Climbing Stairs	Python	Easy 🥉	Array	Recursion, Dynamic Programming
1337	The K Weakest Rows in a Matrix 🔒	Python	Easy 🥉	Array, Heap	Binary Search
1351	Count Negative Numbers in a Sorted Matrix	Python	Easy 🥉	Array	Binary Search
0046	Permutations 🔒	Python	Medium 🥈	Array	Recursion, Backtracking
0048	Rotate Image	Python	Medium 🥈	Array
0078	Subsets	Python	Medium 🥈	Array	Backtracking, Bit Manipulation
0189	Rotate Array	Python	Medium 🥈	Array
0198	House Robber 🔒	Python	Medium 🥈	Array	Recursion, Dynamic Programming
0238	Product of Array Except Self	Python	Medium 🥈	Array	Two Pointers
0322	Coin Change	Python	Medium 🥈	Array, Hash Table	Dynamic Programming, Recursion, Sort

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Stack and Queue

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0020	Valid Parentheses	Python	Easy 🥉	String, Stack
0155	Min Stack 🔒	Python	Easy 🥉	Stack, Heaps
0232	Implement Queue using Stacks	Python	Easy 🥉	Stack, Queue

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Hash Table

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0001	Two Sum	Python	Easy 🥉	Array, Hash Table
0136	Single Number	Python	Easy 🥉	Hash Table	Bit Manipulation
0141	Linked List Cycle	Python	Easy 🥉	Linked List, Hash Table	Two Pointers
0160	Intersection of Two Linked Lists	Python	Easy 🥉	Linked List, Hash Table	Two Pointers
0169	Majority Element	Python	Easy 🥉	Array, Hash Table	Sort
0202	Happy Number 🔒	Python	Easy 🥉	Hash Table
0217	Contains Duplicate	Python	Easy 🥉	Array, Hash Table	Sort
0242	Valid Anagram	Python	Easy 🥉	Array, Hash Table	Sort
0268	Missing Number	Python	Easy 🥉	Array, Hash Table	Sort, Bit Manipulation
0349	Intersection of Two Arrays	Python	Easy 🥉	Array, Hash Table	Sort, Binary Search, Two Pointers
0350	Intersection of Two Arrays II 🔒	Python	Easy 🥉	Array, Hash Table	Sort, Two Pointers
0387	First Unique Character in a String	Python	Easy 🥉	String, Hash Table
0448	Find All Numbers Disappeared in an Array 🔒	Python	Easy 🥉	Array, Hash Table
0771	Jewels and Stones 🔒	Python	Easy 🥉	Hash Table
0003	Longest Substring Without Repeating Characters 🔒	Python	Medium 🥈	String, Hash Table	Sliding Windows
0236	Lowest Common Ancestor of a Binary Tree	Python	Medium 🥈	Tree, Hash Table	Recursion, DFS
0322	Coin Change	Python	Medium 🥈	Array, Hash Table	Dynamic Programming, Recursion, Sort
0347	Top K Frequent Elements	Python	Medium 🥈	Heaps, Hash Table	Sort

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Linked list

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0021	Merge Two Sorted Lists 🔒	Python	Easy 🥉	Linked list	Recursion, Two Pointers
0083	Remove Duplicates from Sorted List	Python	Easy 🥉	Linked List	Two Pointers
0141	Linked List Cycle	Python	Easy 🥉	Linked List, Hash Table	Two Pointers
0160	Intersection of Two Linked Lists	Python	Easy 🥉	Linked List, Hash Table	Two Pointers
0206	Reverse Linked List	Python	Easy 🥉	Linked List	Recursion, Two Pointers
0234	Palindrome Linked List 🔒	Python	Easy 🥉	Linked List	Two Pointers
0876	Middle of the Linked List	Python	Easy 🥉	Linked Lists	Two Pointers
1290	Convert Binary Number in a Linked List to Integer	Python	Easy 🥉	Linked Lists	Recursion, Bit Manipulation
0002	Add Two Numbers	Python	Medium 🥈	Linked Lists	Recursion, Two Pointers

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Heap

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0155	Min Stack 🔒	Python	Easy 🥉	Stack, Heaps
0703	Kth Largest Element in a Stream	Python	Easy 🥉	Heap
1337	The K Weakest Rows in a Matrix 🔒	Python	Easy 🥉	Array, Heap	Binary Search
0347	Top K Frequent Elements	Python	Medium 🥈	Heaps, Hash Table	Sort

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Tree

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0100	Same Tree	Python	Easy 🥉	Tree	Recursion, DFS
0101	Symmetric Tree	Python	Easy 🥉	Tree	Recursion
0104	Maximum Depth of Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0108	Convert Sorted Array to Binary Search Tree 🔒	Python	Easy 🥉	Tree	Recursion
0110	Balanced Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0111	Minimum Depth of Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0112	Path Sum  🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0226	Invert Binary Tree	Python	Easy 🥉	Tree	Recursion
0235	Lowest Common Ancestor of a Binary Search Tree	Python	Easy 🥉	Tree	Recursion
0257	Binary Tree Paths 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0543	Diameter of Binary Tree	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0559	Maximum Depth of N-ary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0572	Subtree of Another Tree	Python	Easy 🥉	Tree, String	Recursion
0589	N-ary Tree Preorder Traversal 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0590	N-ary Tree Postorder Traversal 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0617	Merge Two Binary Trees	Python	Easy 🥉	Tree	Recursion, DFS
0669	Trim a Binary Search Tree	Python	Easy 🥉	Tree	Recursion, DFS
0700	Search in a Binary Search Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0897	Increasing Order Search Tree	Python	Easy 🥉	Tree	Recursion, DFS
0938	Range Sum of BST 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0965	Univalued Binary Tree	Python	Easy 🥉	Tree	Recursion, DFS, BFS
1022	Sum of Root To Leaf Binary Numbers	Python	Easy 🥉	Tree	Recursion, DFS, BFS, Bit Manipulation
0094	Binary Tree Inorder Traversal	Python	Medium 🥈	Tree	Recursion
0230	Kth Smallest Element in a BST	Python	Medium 🥈	Tree	Recursion
0236	Lowest Common Ancestor of a Binary Tree	Python	Medium 🥈	Tree, Hash Table	Recursion, DFS

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By implementation

Search

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0035	Search Insert Position 🔒	Python	Easy 🥉	Array	Binary Search
0100	Same Tree	Python	Easy 🥉	Tree	Recursion, DFS
0104	Maximum Depth of Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0110	Balanced Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0111	Minimum Depth of Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0112	Path Sum  🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0257	Binary Tree Paths 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0349	Intersection of Two Arrays	Python	Easy 🥉	Array, Hash Table	Sort, Binary Search, Two Pointers
0392	Is Subsequence 🔒	Python	Easy 🥉	String	Two Pointers, Greedy, Recursion, Dynamic Programming, Binary Search
0543	Diameter of Binary Tree	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0559	Maximum Depth of N-ary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0589	N-ary Tree Preorder Traversal 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0590	N-ary Tree Postorder Traversal 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0617	Merge Two Binary Trees	Python	Easy 🥉	Tree	Recursion, DFS
0669	Trim a Binary Search Tree	Python	Easy 🥉	Tree	Recursion, DFS
0700	Search in a Binary Search Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0704	Binary Search	Python	Easy 🥉	Array	Binary Search, Recursion
0897	Increasing Order Search Tree	Python	Easy 🥉	Tree	Recursion, DFS
0938	Range Sum of BST 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0965	Univalued Binary Tree	Python	Easy 🥉	Tree	Recursion, DFS, BFS
1022	Sum of Root To Leaf Binary Numbers	Python	Easy 🥉	Tree	Recursion, DFS, BFS, Bit Manipulation
1337	The K Weakest Rows in a Matrix 🔒	Python	Easy 🥉	Array, Heap	Binary Search
1351	Count Negative Numbers in a Sorted Matrix	Python	Easy 🥉	Array	Binary Search

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Sort

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0169	Majority Element	Python	Easy 🥉	Array, Hash Table	Sort
0217	Contains Duplicate	Python	Easy 🥉	Array, Hash Table	Sort
0242	Valid Anagram	Python	Easy 🥉	Array, Hash Table	Sort
0268	Missing Number	Python	Easy 🥉	Array, Hash Table	Sort, Bit Manipulation
0349	Intersection of Two Arrays	Python	Easy 🥉	Array, Hash Table	Sort, Binary Search, Two Pointers
0350	Intersection of Two Arrays II 🔒	Python	Easy 🥉	Array, Hash Table	Sort, Two Pointers
0322	Coin Change	Python	Medium 🥈	Array, Hash Table	Dynamic Programming, Recursion, Sort
0347	Top K Frequent Elements	Python	Medium 🥈	Heaps, Hash Table	Sort

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Greedy

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0122	Best Time to Buy and Sell Stock II	Python	Easy 🥉	Array	Greedy
0392	Is Subsequence 🔒	Python	Easy 🥉	String	Two Pointers, Greedy, Recursion, Dynamic Programming, Binary Search

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Divide and Conquer

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0053	Maximum Subarray 🔒	Python	Easy 🥉	Array	Dynamic Programming, Divide and Conquer, Recursion

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Recursion

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0021	Merge Two Sorted Lists 🔒	Python	Easy 🥉	Linked list	Recursion, Two Pointers
0053	Maximum Subarray 🔒	Python	Easy 🥉	Array	Dynamic Programming, Divide and Conquer, Recursion
0070	Climbing Stairs	Python	Easy 🥉		Recursion, Dynamic Programming
0100	Same Tree	Python	Easy 🥉	Tree	Recursion, DFS
0101	Symmetric Tree	Python	Easy 🥉	Tree	Recursion
0104	Maximum Depth of Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0108	Convert Sorted Array to Binary Search Tree 🔒	Python	Easy 🥉	Tree	Recursion
0110	Balanced Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0111	Minimum Depth of Binary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0112	Path Sum  🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0118	Pascal's Triangle	Python	Easy 🥉	Array	Recursion, Dynamic Programming
0206	Reverse Linked List	Python	Easy 🥉	Linked List	Recursion, Two Pointers
0226	Invert Binary Tree	Python	Easy 🥉	Tree	Recursion
0235	Lowest Common Ancestor of a Binary Search Tree	Python	Easy 🥉	Tree	Recursion
0257	Binary Tree Paths 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0392	Is Subsequence 🔒	Python	Easy 🥉	String	Two Pointers, Greedy, Recursion, Dynamic Programming, Binary Search
0543	Diameter of Binary Tree	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0559	Maximum Depth of N-ary Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0572	Subtree of Another Tree	Python	Easy 🥉	Tree, String	Recursion
0589	N-ary Tree Preorder Traversal 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0590	N-ary Tree Postorder Traversal 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0617	Merge Two Binary Trees	Python	Easy 🥉	Tree	Recursion, DFS
0669	Trim a Binary Search Tree	Python	Easy 🥉	Tree	Recursion, DFS
0700	Search in a Binary Search Tree 🔒	Python	Easy 🥉	Tree	Recursion, DFS
0704	Binary Search	Python	Easy 🥉	Array	Binary Search, Recursion
0746	Min Cost Climbing Stairs	Python	Easy 🥉	Array	Recursion, Dynamic Programming
0897	Increasing Order Search Tree	Python	Easy 🥉	Tree	Recursion, DFS
0938	Range Sum of BST 🔒	Python	Easy 🥉	Tree	Recursion, DFS, BFS
0965	Univalued Binary Tree	Python	Easy 🥉	Tree	Recursion, DFS, BFS
1022	Sum of Root To Leaf Binary Numbers	Python	Easy 🥉	Tree	Recursion, DFS, BFS, Bit Manipulation
1290	Convert Binary Number in a Linked List to Integer	Python	Easy 🥉	Linked Lists	Recursion, Bit Manipulation
0002	Add Two Numbers	Python	Medium 🥈	Linked Lists	Recursion, Two Pointers
0022	Generate Parentheses	Python	Medium 🥈	String	Recursion, Backtracking, Dynamic Programming
0046	Permutations 🔒	Python	Medium 🥈	Array	Recursion, Backtracking
0094	Binary Tree Inorder Traversal	Python	Medium 🥈	Tree	Recursion
0198	House Robber 🔒	Python	Medium 🥈	Array	Recursion, Dynamic Programming
0230	Kth Smallest Element in a BST	Python	Medium 🥈	Tree	Recursion
0236	Lowest Common Ancestor of a Binary Tree	Python	Medium 🥈	Tree, Hash Table	Recursion, DFS
0322	Coin Change	Python	Medium 🥈	Array, Hash Table	Dynamic Programming, Recursion, Sort

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Dynamic Programming

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0053	Maximum Subarray 🔒	Python	Easy 🥉	Array	Dynamic Programming, Divide and Conquer, Recursion
0070	Climbing Stairs	Python	Easy 🥉	Integer	Recursion, Dynamic Programming
0118	Pascal's Triangle	Python	Easy 🥉	Array	Recursion, Dynamic Programming
0121	Best Time to Buy and Sell Stock	Python	Easy 🥉	Array	Dynamic Programming
0392	Is Subsequence 🔒	Python	Easy 🥉	String	Two Pointers, Greedy, Recursion, Dynamic Programming, Binary Search
0746	Min Cost Climbing Stairs	Python	Easy 🥉	Array	Recursion, Dynamic Programming
0005	Longest Palindromic Substring	Python	Medium 🥈	String	Dynamic Programming
0022	Generate Parentheses	Python	Medium 🥈	String	Recursion, Dynamic Programming
0198	House Robber 🔒	Python	Medium 🥈	Array	Recursion, Dynamic Programming
0322	Coin Change	Python	Medium 🥈	Array, Hash Table	Dynamic Programming, Recursion, Sort
0338	Counting Bits 🔒	Python	Medium 🥈	Binary Number	Bit Manipulation, Dynamic Programming

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Backtracking

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0022	Generate Parentheses	Python	Medium 🥈	String	Recursion, Backtracking, Dynamic Programming
0046	Permutations 🔒	Python	Medium 🥈	Array	Recursion, Backtracking
0078	Subsets	Python	Medium 🥈	Array	Backtracking, Bit Manipulation

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Two Pointers and Sliding Windows

#	Title	Solution	Difficulty	Data Structure	Paradigm & Implementation
0021	Merge Two Sorted Lists 🔒	Python	Easy 🥉	Linked list	Recursion, Two Pointers
0083	Remove Duplicates from Sorted List	Python	Easy 🥉	Linked List	Two Pointers
0141	Linked List Cycle	Python	Easy 🥉	Linked List, Hash Table	Two Pointers
0160	Intersection of Two Linked Lists	Python	Easy 🥉	Linked List, Hash Table	Two Pointers
0206	Reverse Linked List	Python	Easy 🥉	Linked List	Recursion, Two Pointers
0234	Palindrome Linked List 🔒	Python	Easy 🥉	Linked List	Two Pointers
0283	Move Zeroes	Python	Easy 🥉	Array	Two Pointers
0344	Reverse String	Python	Easy 🥉	Array	Two Pointers
0349	Intersection of Two Arrays	Python	Easy 🥉	Array, Hash Table	Sort, Binary Search, Two Pointers
0350	Intersection of Two Arrays II 🔒	Python	Easy 🥉	Array, Hash Table	Sort, Two Pointers
0392	Is Subsequence 🔒	Python	Easy 🥉	String	Two Pointers, Greedy, Recursion, Dynamic Programming, Binary Search
0876	Middle of the Linked List	Python	Easy 🥉	Linked Lists	Two Pointers
0002	Add Two Numbers	Python	Medium 🥈	Linked Lists	Recursion, Two Pointers
0003	Longest Substring Without Repeating Characters 🔒	Python	Medium 🥈	String, Hash Table	Sliding Windows
0238	Product of Array Except Self	Python	Medium 🥈	Array	Two Pointers

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