Problem Statement

At Lyft, you are given an integer array and a target value. 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 [i, j] such that nums[i] + nums[j] == target
• You may assume exactly one valid answer exists
• You may not use the same element twice
• Return the indices in any order

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

Constraints

• 2 <= len(nums) <= 10^4
• -10^9 <= nums[i] <= 10^9
• -10^9 <= target <= 10^9
• Exactly one valid answer exists