Two Sum

Given a list of integers nums and an integer target, return the indices of the two numbers that add up to target.

You may assume each input has exactly one solution, and you may not use the same element twice. Return the answer as a list of two indices in any order.

Example:

Input: nums = [2, 7, 11, 15], target = 9
Output: [0, 1]   # because nums[0] + nums[1] == 9