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.

__Questions to ask yourself__
- Does the input always have the right format?
- Does the input have the right format?
- Does the input have the right range?
- Does the output have the right range?
- Can we assume the input is valid?
- Are there edge cases?
- Are there some cases that we should consider separately?

__Example__

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]

__Pseudocode__