演算法：1.two sum

題目來自

https://leetcode.com/problems/two-sum/description/leetcode.com

Two Sumleetcode.com

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

思路：

時間複雜度 O（n）

空間複雜度 O(n)