n的阶乘末尾0 [LeetCode 172. 阶乘后的零](https://leetcode-cn.com/problems/factorial-trailing-zeroes/)
路径是否相交 [LeetCode 1496.判断路径是否相交](https://leetcode-cn.com/problems/path-crossing/) 
判断字符串括号是否匹配 [LeetCode 20. 有效的括号](https://leetcode-cn.com/problems/valid-parentheses/)