Linked List Palindrome

Check if a linked list is a palindrome.

Difficulty: Medium

Copy List with Random Pointer

Create a deep copy of a linked list with random pointers.

Difficulty: Hard

Reverse Nodes in K Group

Reverse nodes in a linked list K at a time.

Difficulty: Hard

Best Time to Buy and Sell Stock

Beat the stock market. Find optimal times to buy and sell.

Difficulty: Easy

Majority Element

A majority element always exists, can you find it?

Difficulty: Medium

Jump Game

Can you jump from the start of the array to the end?

Difficulty: Hard

Number of Islands

How many islands are there in this made up map?

Difficulty: Hard

Move Zeroes

Move all zeros to the end of the array in place.

Difficulty: Easy

Search In Rotated Array

Sorted array, but with a twist...

Difficulty: Easy

3Sum

Find all unique triplets in the array which gives the sum of zero.

Difficulty: Medium

Merge K Sorted Lists

K lists, all sorted. Merge them into a single list.

Difficulty: Very Hard

Nth Fibonacci

Calculate the Nth Fibonacci Number.

Difficulty: Easy

Edit Distance

How many moves to convert one string to another?

Difficulty: Very Hard

Balanced Binary Tree

Is the binary tree balanced?

Difficulty: Easy

Validate Binary Search Tree

Given a tree, can you confirm it is a **binary search** tree?

Difficulty: Medium

Flatten Binary Tree to Linked List

Turn the Binary Tree into a Linked List

Difficulty: Very Hard

Min Stack

Stacks are cool, but whats the minimum value in the stack?

Difficulty: Medium

K-Closest Points

Find the K Closests Points to the origin

Difficulty: Hard

Largest Rectangle in Histogram

Find the largest rectangle using the bars in a Histogram

Difficulty: Very Hard

LRU Cache

Least Recently Used Cache : Most Frequent Interview Question

Difficulty: Very Hard

Group Anagrams

Group anagrams into lists.

Difficulty: Easy

Minimum Window Substring

Find all characters of string Y in string X.

Difficulty: Very Hard

Longest Palindromic Substring

Longest palindrome you can find in a string.

Difficulty: Very Hard

Find The Duplicate Number

Given numbers 1 to n and a repeated number, find the repeat.

Difficulty: Easy

Letter Combinations of a Phone Number

Find all combinations of a number.

Difficulty: Medium

Trapping Rain Water

You poured water over a bar graph, how much water did you catch?

Difficulty: Very Hard