Given an array of integers nums and an integer target, return the indices of the two distinct elements whose sum equals target. Return the indices in any order. You may assume exactly one valid pair exists, and the same element cannot be used twice.
Input: nums = [2, 7, 11, 15], target = 9
Output: [0, 1]
Explanation: nums[0] + nums[1] = 2 + 7 = 9
Input: nums = [3, 2, 4], target = 6
Output: [1, 2]
Explanation: nums[1] + nums[2] = 2 + 4 = 6
2 <= len(nums) <= 10^5-10^9 <= nums[i] <= 10^9-10^9 <= target <= 10^9