阶乘末尾0的个数

统计2和5的因子个数，取较小值即可：

import java.util.*;
public class Main {
    public static void main(String[] args) throws Exception{
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int two = 0, five = 0;
        for(int i = 2; i <= n; ++i){
            two += f(i, 2);
            five += f(i, 5);
        }
        System.out.println(Math.min(two, five));    //2和5的个数取较小值
    }
    static int f(int a, int b){    //统计a含几个b因子
        int r = 0;
        while(a%b == 0){
            r++;
            a = a/b;
        }
        return r;
    }
}