Two Sum Index Lookup

Problem

Given an integer array nums and an integer target, return the indices of the two distinct elements whose values add up to target. Return the indices as a list of two integers in any order. You may assume exactly one valid answer exists.

Constraints

• 2 <= len(nums) <= 10^5
• -10^9 <= nums[i] <= 10^9
• -10^9 <= target <= 10^9
• Exactly one valid pair exists
• You may not use the same element twice