Given an array of integers nums and an integer target, return the indices of the two different elements whose values add up to target.
Exactly one valid answer exists. Return the two indices in increasing order.
Inputnums = [2, 7, 11, 15], target = 9
Output[0, 1]
nums[0] + nums[1] equals 9.
Inputnums = [3, 2, 4], target = 6
Output[1, 2]
2 ≤ nums.length ≤ 10,000