https://blog.csdn.net/my_sunshine26/article/details/72849441
https://blog.csdn.net/my_sunshine26/article/details/72849441
题目：
1.
http://poj.org/problem?id=3169
2.
http://poj.org/problem?id=1716
3.
http://poj.org/problem?id=1201
原文：https://www.cnblogs.com/cmyg/p/9557681.html