A7974.阶乘

递归求阶乘，时间复杂度 $O(n)$

#include <cstdio>
using namespace std;

int n;

//求阶乘
int f(int n) {
    if (n == 0) return 1;//0! = 1
    return n*f(n-1);//10! = 10*9!
}

int main() {
    scanf("%d", &n);
    printf("%d", f(n));
    return 0;
}