https://blog.csdn.net/qq_39504764/article/details/94833418
https://blog.csdn.net/da_kao_la/article/details/79913459
https://www.cnblogs.com/yun-an/p/11108072.html
https://www.bbsmax.com/A/gGdXnkPWJ4/
https://www.jianshu.com/p/e800b2de4810
https://blog.csdn.net/qq_36206070/article/details/97618703
链表 https://www.cnblogs.com/zyb993963526/p/7544827.html
找数字
https://blog.csdn.net/qq_43408238/article/details/87626477
log10(i)+1