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Easy
Arrays
Hash Table
Two Sum Problem
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
12,453 participants50 credits
Deadline2 days left
Medium
Tree
BFS
Binary Tree Level Order Traversal
Given the root of a binary tree, return the level order traversal of its nodes' values.
8,765 participants100 credits
Deadline3 days left
Hard
Linked List
Divide and Conquer
Heap
Merge K Sorted Lists
You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.
5,432 participants200 credits
Deadline5 days left
Easy
Stack
String
Valid Parentheses
Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
15,678 participants50 credits
Deadline1 day left
Medium
Hash Table
Linked List
Design
LRU Cache
Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.
7,654 participants150 credits
Deadline4 days left
Hard
Backtracking
Trie
Word Search II
Given an m x n board of characters and a list of strings words, return all words on the board.
4,321 participants250 credits
Deadline6 days left
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Your Stats
Your competition performance
Global Rank#87
Total Score4,320
Challenges Completed24
Win Rate68%