区分N和L怎么这么难。

https://jingyan.baidu.com/album/6dad507505da14a123e36ea5.html?picindex=5

https://wenku.baidu.com/view/1cc834d6b8d528ea81c758f5f61fb7360b4c2b87.html

原文地址:https://www.cnblogs.com/maowuyu-xb/p/10766531.html