Given a string, find the length of the longest substring without repeating characters.
Given "abcabcbb", the answer is "abc", which the length is 3.
You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit.
Add the two numbers and return it as a linked list.
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution.
Given nums = [2, 7, 11, 15], target = 9,