LeetCode – Refresh – Factorial Trailing Zeroes

Think about that.. n! = n * (n-1) * (n-2) ..... *1

Zeros happened when each of them can be divided by 10. And 10 = 2 * 5. 2 is much more than 5 in the number mutilpication. Then just use 5 as the factor.

But one more thing need to notice:

Use n /= 5 for every loop instead of i += 5; It can overflow.

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