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100 problems across 21 topics. Select one to start coding.
All (100)
Easy (35)
Medium (45)
Hard (20)
All Topics
100
Array
47
String
21
Hash Table
15
DP
22
Sorting
15
Tree
12
Graph
6
Binary Search
8
Two Pointers
12
Sliding Window
3
Stack
8
Heap
6
Linked List
5
Backtracking
9
Matrix
11
Greedy
4
Math
8
Bit Manipulation
5
Recursion
11
BFS
11
1
Two Sum
Easy
Array
hashmap
2
Reverse String
Easy
String
Two Pointers
3
Valid Parentheses
Easy
Stack
String
4
Climbing Stairs
Easy
DP
5
Binary Search
Easy
Binary Search
Array
6
Best Time to Buy and Sell Stock
Easy
Array
DP
7
Valid Anagram
Easy
String
Hash Table
Sorting
8
Contains Duplicate
Easy
Array
Hash Table
Sorting
9
Merge Two Sorted Lists
Easy
Linked List
Recursion
10
Maximum Depth of Binary Tree
Easy
Tree
Recursion
BFS
11
Invert Binary Tree
Easy
Tree
Recursion
BFS
12
Palindrome Number
Easy
Math
13
Roman to Integer
Easy
String
Hash Table
Math
14
Longest Common Prefix
Easy
String
15
Remove Duplicates from Sorted Array
Easy
Array
Two Pointers
16
Reverse Linked List
Easy
Linked List
Recursion
17
Symmetric Tree
Easy
Tree
Recursion
BFS
18
Single Number
Easy
Array
Bit Manipulation
19
Intersection of Two Arrays II
Easy
Array
Hash Table
Sorting
20
Move Zeroes
Easy
Array
Two Pointers
21
Plus One
Easy
Array
Math
22
Missing Number
Easy
Array
Math
Bit Manipulation
23
Power of Two
Easy
Math
Bit Manipulation
24
Valid Palindrome
Easy
String
Two Pointers
25
Majority Element
Easy
Array
Hash Table
Sorting
26
Number of 1 Bits
Easy
Bit Manipulation
27
Subtree of Another Tree
Easy
Tree
Recursion
28
Range Sum Query
Easy
Array
DP
29
Diameter of Binary Tree
Easy
Tree
Recursion
30
Min Stack
Easy
Stack
31
Flood Fill
Easy
Matrix
BFS
Graph
32
Middle of the Linked List
Easy
Linked List
Two Pointers
33
Squares of a Sorted Array
Easy
Array
Two Pointers
Sorting
34
Backspace String Compare
Easy
String
Stack
Two Pointers
35
First Bad Version
Easy
Binary Search
36
Maximum Subarray
Medium
Array
DP
37
Merge Intervals
Medium
Array
Sorting
38
Longest Substring Without Repeating Characters
Medium
String
Sliding Window
39
Product of Array Except Self
Medium
Array
40
Linked List Cycle
Medium
Linked List
Two Pointers
41
Three Sum
Medium
Array
Two Pointers
Sorting
42
Container With Most Water
Medium
Array
Two Pointers
Greedy
43
Group Anagrams
Medium
String
Hash Table
Sorting
44
Coin Change
Medium
Array
DP
45
Number of Islands
Medium
Matrix
BFS
Graph
46
Sort Colors
Medium
Array
Two Pointers
Sorting
47
Search in Rotated Sorted Array
Medium
Array
Binary Search
48
Rotate Image
Medium
Array
Matrix
Math
49
Spiral Matrix
Medium
Array
Matrix
50
Set Matrix Zeroes
Medium
Array
Matrix
Hash Table
51
Jump Game
Medium
Array
Greedy
DP
52
Unique Paths
Medium
Math
DP
Matrix
53
Word Search
Medium
Matrix
Backtracking
54
Decode Ways
Medium
String
DP
55
Validate Binary Search Tree
Medium
Tree
Recursion
56
Binary Tree Level Order Traversal
Medium
Tree
BFS
57
Construct Binary Tree from Preorder and Inorder Traversal
Medium
Tree
Recursion
Hash Table
58
Kth Smallest Element in a BST
Medium
Tree
Binary Search
59
Lowest Common Ancestor of a Binary Search Tree
Medium
Tree
Recursion
60
Course Schedule
Medium
Graph
BFS
DP
61
Implement Trie (Prefix Tree)
Medium
String
Hash Table
62
Combination Sum
Medium
Array
Backtracking
63
Subsets
Medium
Array
Backtracking
Bit Manipulation
64
Permutations
Medium
Array
Backtracking
65
Letter Combinations of a Phone Number
Medium
String
Backtracking
66
Generate Parentheses
Medium
String
Backtracking
67
House Robber
Medium
Array
DP
68
House Robber II
Medium
Array
DP
69
Longest Increasing Subsequence
Medium
Array
DP
Binary Search
70
Partition Equal Subset Sum
Medium
Array
DP
71
Top K Frequent Elements
Medium
Array
Hash Table
Heap
Sorting
72
Find Peak Element
Medium
Array
Binary Search
73
Kth Largest Element in an Array
Medium
Array
Heap
Sorting
74
Task Scheduler
Medium
Array
Hash Table
Greedy
Heap
75
Daily Temperatures
Medium
Array
Stack
76
Evaluate Reverse Polish Notation
Medium
Array
Stack
Math
77
Minimum Path Sum
Medium
Array
Matrix
DP
78
Clone Graph
Medium
Graph
BFS
Hash Table
79
Pacific Atlantic Water Flow
Medium
Matrix
BFS
Graph
80
Gas Station
Medium
Array
Greedy
81
Trapping Rain Water
Hard
Array
Two Pointers
Stack
DP
82
Merge K Sorted Lists
Hard
Linked List
Heap
Sorting
83
Minimum Window Substring
Hard
String
Hash Table
Sliding Window
84
Serialize and Deserialize Binary Tree
Hard
Tree
String
BFS
85
Word Ladder
Hard
String
BFS
Hash Table
86
Median of Two Sorted Arrays
Hard
Array
Binary Search
87
Longest Valid Parentheses
Hard
String
Stack
DP
88
Sudoku Solver
Hard
Matrix
Backtracking
89
N-Queens
Hard
Backtracking
Matrix
90
Edit Distance
Hard
String
DP
91
Maximum Profit in Job Scheduling
Hard
Array
Binary Search
DP
Sorting
92
Sliding Window Maximum
Hard
Array
Heap
Sliding Window
93
Alien Dictionary
Hard
String
Graph
Sorting
94
Word Break II
Hard
String
DP
Backtracking
95
Regular Expression Matching
Hard
String
DP
96
Burst Balloons
Hard
Array
DP
97
Largest Rectangle in Histogram
Hard
Array
Stack
98
Binary Tree Maximum Path Sum
Hard
Tree
DP
Recursion
99
Longest Consecutive Sequence
Hard
Array
Hash Table
100
Find Median from Data Stream
Hard
Heap
Sorting