nyoj-451-光棍节的快乐（错排公式）

 题目链接

 /*
     Name:nyoj-451-光棍节的快乐
     Copyright:
     Author:
     Date: 2018/4/25 16:44:47
     Description:D(n)=(n-1)*(D(n-1)*D(n-2))[D[0]=0;D[1]=1]
 */
 #include <iostream>
 #include <cstdio>
 using namespace std;
 long long c[][], wrongsort[];

 int main()
 {
     for (int i=; i<=; i++) {//阶乘打表
         c[i][] = c[i][i] = ;
         for (int j=; j<i; j++) {
             c[i][j] = c[i-][j] + c[i-][j-];
         }
     }
     wrongsort[] = ;
     wrongsort[] = ;
     for (int i=; i<=; i++) {//错排打表
         wrongsort[i] = (i-) * (wrongsort[i-] + wrongsort[i-]);
     }
     int n,m;
     while (cin>>n>>m) {
         cout<<c[n][n-m]*wrongsort[m]<<endl;
     }
     return ;
 }