Given an array of strings strs, group the anagrams together. You can return the answer in any order.
Given the head of a singly linked list, reverse the list, and return the reversed list.
Given a string s, find the length of the longest substring without repeating characters.
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 input would have exactly one solution, and you may not use the same element twice.