字符串比较大小
https://blog.csdn.net/jason_cuijiahui/article/details/79038468
http://www.cplusplus.com/reference/string/string/compare/
https://blog.csdn.net/Allenlzcoder/article/details/78254693
【Leetcode】最大的数
原文：https://www.cnblogs.com/gdut-gordon/p/11703114.html
