哈希表

微信推文 https://mp.weixin.qq.com/s/g8N6WmoQmsCUw3_BaWxHZA

JAVA中Map的用法 https://www.cnblogs.com/xiaostudy/p/9510763.html 

力扣练习题1  https://leetcode-cn.com/problems/two-sum/submissions/