Problem
Given an integer array and a target, return the indices of the two numbers that sum to the target. Exactly one solution exists and an element may not be reused.
Input / Output
- Input: int array nums, int target.
- Output: the two indices (any order).
Constraints
- 2 ≤ n ≤ 10^4; values may be negative.
- An O(n) solution is expected over the O(n^2) brute force.
Example
- nums = [2,7,11,15], target = 9 → [0,1].
- nums = [3,3], target = 6 → [0,1].