leetcode Factorial Trailing Zeroes

没什么意思的题目。

https://leetcode.com/problems/factorial-trailing-zeroes/

参考：

http://bookshadow.com/weblog/2014/12/30/leetcode-factorial-trailing-zeroes/

自己的code，效率低。

my code:

        if n == 0:
            return 0
            
        def fac(m):
            if m == 0:
                return 1
            else:
                return m * fac(m - 1)

        num = str(fac(n))
        i = -1
        while num[i] == '0':
            #print count
            i -= 1
        
        
        return len(num[i+1:])