Problem description:

Given a non-empty array of integers, return the k most frequent elements.

Problem description:

Given an array of strings, group anagrams together.

Problem description:

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.
Return a deep copy of the list.

Problem description:

TinyURL is a URL shortening service where you enter a URL such as https://leetcode.com/problems/design-tinyurl and it returns a short URL such as http://tinyurl.com/4e9iAk.

Problem description:

Given a string, find the length of the longest substring T that contains at most k distinct characters.

Problem description:

Given a string s , find the length of the longest substring t that contains at most 2 distinct characters.

Problem description:

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

Problem description:

/*
Given an array of non-negative integers, you are initially positioned at the first index of the array.

Problem description:

Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Problem description:

A peak element is an element that is greater than its neighbors.