172. Factorial Trailing Zeroes

• Difficulty: Easy

• Topics: Math

• Similar Questions:

  • Number of Digit One

  • Preimage Size of Factorial Zeroes Function

Problem:

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.

Note: Your solution should be in logarithmic time complexity.

Solutions:

class Solution {
public:
    int trailingZeroes(int n) {
        int count = 0;
        int divisor = 5;
        while (n >= divisor) {
            count += n/divisor;
            n /= 5; // be careful about overflow!
        } 

        return count;
    }
};