Problem

At Stripe, you are given an unsorted integer array nums and an integer target. Write a function that returns the indices of the two distinct elements whose values add up to target.

You may assume there is exactly one valid pair, and you may not use the same element twice.

Formal Specification

• Input:
  • nums: list of integers
  • target: integer
• Output:
  • A list of two integers [i, j] where i != j and nums[i] + nums[j] == target

Examples

Example 1

• Input: nums = [2, 7, 11, 15], target = 9
• Output: [0, 1]
• Explanation: nums[0] + nums[1] = 2 + 7 = 9

Example 2

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

Example 3

• Input: nums = [3, 3], target = 6
• Output: [0, 1]
• Explanation: The two different indices contain the same value.

Constraints

• 2 <= len(nums) <= 10^5
• -10^9 <= nums[i] <= 10^9
• -10^9 <= target <= 10^9
• Exactly one valid answer exists