Two Sum

Problem

Given an array of integers nums and an integer target, return the indices [i, j] of the two numbers that add up to target. Exactly one solution always exists; you may not use the same element twice. Example: nums=[2,7,11,15], target=9 → [0,1] because nums[0]+nums[1]=9.

Constraints

• ›2 ≤ nums.length ≤ 10⁴
• ›-10⁹ ≤ nums[i] ≤ 10⁹
• ›Exactly one valid answer exists