Given an array 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.
**Example 1:**
```
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: nums[0] + nums[1] == 9
```
**Example 2:**
```
Input: nums = [3,2,4], target = 6
Output: [1,2]
```