摘要：
There are three problems in hackrank. two sum http request to get title binary search （find first large/small element）(网上没有一个现成运行的代码) 都是些不是很难的题， 但是因为是 阅读全文
摘要：
1. Solution: add popmax this func, you can pop out max at any time , so max stack to track the max elements does not work as minstack(leetcode 155) di 阅读全文