172. Factorial Trailing Zeroes

Factorial Trailing Zeroes - LeetCode

Given an integer n, return the number of trailing zeroes in n!. Example 1: Input: 3 Output: 0 Explanation: 3! = 6, no trailing zero. Example 2: Input: 5 Output: 1 Explanation: 5! = 120, one trailing zero.

• code

class Solution:
    def trailingZeroes(self, n: int) -> int:
        res = 0
        while n >= 5:
            res += n // 5
            n //= 5
        return res

Zeros come from 10 which is 25, and 5>2, so we just need to count how many 5 this factorial has. ( Once has a 5, must has 2, must has 0) 25: 6 because 25=55