1. Two Sum

Given an array of integers nums and an integer target, return the indices (0-based) of the two numbers that add up to target. Exactly one valid answer exists and you may not use the same element twice. Return the two indices in ascending order.

4
2 7 11 15
9

0 1

3
3 2 4
6

1 2

I/O Format

Input: line 1 = n, line 2 = n space-separated integers, line 3 = target.
Output: the two indices separated by a space.

Constraints:

• 2 ≤ n ≤ 10^4
• -10^9 ≤ nums[i], target ≤ 10^9
• Exactly one solution