1. Two Sum
Given an integer array nums and an integer target, return the indices of the two numbers that add up to target.
Each input has exactly one valid answer, and you may not use the same element twice.
範例 1:
輸入： nums = [2,7,11,15], target = 9 輸出： [0,1]
範例 2:
輸入： nums = [3,2,4], target = 6 輸出： [1,2]
限制條件：
2 <= nums.length <= 10^4Exactly one valid answer exists.