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.
You can return the answer in any order.
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
Input: nums = [3,2,4], target = 6
Output: [1,2]
Explanation: Because nums[1] + nums[2] == 6, we return [1, 2].
Input: nums = [3,3], target = 6
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 6, we return [0, 1].