摘要：
HashMap和HashSet的区别是Java面试中最常被问到的问题。如果没有涉及到Collection框架以及多线程的面试，可以说是不完整。而Collection框架的问题不涉及到HashSet和HashMap，也可以说是不完整。HashMap和HashSet都是collection框架的一部分， 阅读全文
摘要：
Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are n 阅读全文