172.阶乘后的零

方法：

class Solution {public int trailingZeroes(int n) {int ans = 0;for(int i = 5;i<=n;i+=5){for(int x = i; x % 5==0; x/=5){++ans;}}return ans;}
}

进一步优化：

class Solution {public int trailingZeroes(int n) {int ans = 0;while (n != 0) {n /= 5;ans += n;}return ans;}
}