Two Sum with Target

At Stripe, you are given a list of transaction values and a target amount. Return the indices of the two distinct elements whose sum equals the target.

Formal Specification

Implement a function two_sum(nums, target) where:

• nums is a list of integers
• target is an integer
• Return a list of two integers representing the indices of the matching pair

You may assume:

1. Exactly one valid pair exists.
2. You may not use the same element twice.
3. The returned indices can be in any order.