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, and you may not use the same element twice.
Example:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
https://leetcode.com/problems/two-sum/
Solution: https://github.com/kiote/cpp-small-projects/blob/master/leetCode/easy-algs/twoSum.py O(N^2)