Data Structures &amp; Algorithms

LRU Cache

#146

MediumStack & Queue

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class with get and put operations in...

O(1) / O(capacity)

Merge Intervals

#56

MediumIntervals

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals...

O(n log n) / O(n)

N-Queens

#51

HardBacktracking

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n, return al...

O(n!) / O(n²)

Permutations

#46

MediumBacktracking

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order....

O(n! * n) / O(n)

Subsets

#78

MediumBacktracking

Given an integer array nums of unique elements, return all possible subsets (the power set). The solution set must not contain duplicate subsets....

O(n * 2^n) / O(n)

Word Ladder

#127

HardGraphs

A transformation sequence from beginWord to endWord using dictionary wordList is a sequence where every adjacent pair of words differs by a single let...

O(M² * N) / O(M * N)

Course Schedule

#207

MediumGraphs

There are a total of numCourses courses you have to take. Some courses may have prerequisites. Given the total number of courses and a list of prerequ...

O(V + E) / O(V + E)

Invert Binary Tree

#226

EasyTrees

Given the root of a binary tree, invert the tree, and return its root....

O(n) / O(h)

Binary Search

#704

EasyBinary Search

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists...

O(log n) / O(1)

Search in Rotated Sorted Array

#33

MediumBinary Search

There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function, nums is possibly rotated at a...

O(log n) / O(1)

Lowest Common Ancestor of BST

#235

MediumTrees

Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST....

O(h) / O(1)

Binary Tree Maximum Path Sum

#124

HardTrees

A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. The path sum of a path i...

O(n) / O(h)

Climbing Stairs

#70

EasyDynamic Programming

You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb ...

Longest Increasing Subsequence

#300

Given an integer array nums, return the length of the longest strictly increasing subsequence....

O(n log n) / O(n)

Word Break

#139

Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary wor...

O(n² * m) / O(n)

Coin Change

#322

O(amount * n) / O(amount)

You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return ...

Edit Distance

#72

Given two strings word1 and word2, return the minimum number of operations required to convert word1 to word2. You have the following three operations...

O(mn) / O(mn)

Valid Palindrome

#125

EasyTwo Pointers

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the ...

Container With Most Water

#11

MediumTwo Pointers

You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i, 0) and (i, hei...

Trapping Rain Water

#42

HardTwo Pointers

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining....

Longest Substring Without Repeating Characters

#3

MediumSliding Window

Given a string s, find the length of the longest substring without repeating characters....

O(n) / O(min(m,n))

Minimum Window Substring

#76

HardSliding Window

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicat...

O(m + n) / O(m + n)

Sliding Window Maximum

#239

HardSliding Window

You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You ca...

O(n) / O(k)

3Sum

#15

MediumTwo Pointers

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k]...

O(n²) / O(1)

Contains Duplicate

#217

EasyArrays & Hashing

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct....

Product of Array Except Self

#238

Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. You must w...

Top K Frequent Elements

#347

Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order....

Group Anagrams

#49

O(n * k log k) / O(n * k)

Given an array of strings strs, group the anagrams together. You can return the answer in any order....

Valid Anagram

#242

EasyArrays & Hashing

Given two strings s and t, return true if t is an anagram of s, and false otherwise. An Anagram is a word or phrase formed by rearranging the letters ...

Longest Consecutive Sequence

#128

Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n...

Two Sum

#1

EasyArrays & Hashing

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. You may assume that each inp...