HDU 2049 - 不容易系列之(4)——考新郎

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2049

#include <stdio.h>int main(void){    int i, m, n;    __int64 a[21][2] = {{1,0},{1,0},{2,1},{6,2}};    for (i = 4; i < 21; i++)    {        a[i][0] = i * a[i-1][0];        a[i][1] = (i-1) * (a[i-1][1] + a[i-2][1]);    }    scanf("%d", &i);    while (i-- && scanf("%d%d", &n, &m))        printf("%I64d\n", a[n][0]/a[m][0]/a[n-m][0]*a[m][1]);    return 0;}