C++ 代码

# include <iostream>
# include <vector>
# include <algorithm>
#include<cmath>
using namespace std;
const int mod = 123456 ;


int main(void)
{
    int n,m;
    cin >> n>>m;
    int dp[600][600]={0};
    for(int i=0;i<=n;++i)dp[i][1]=2;
    for(int i=3; i<=n;++i){
        for(int j=2;j<=i;++j){
            dp[i][j]=(dp[i-1][j]*j+dp[i-1][j-1]*2+dp[i-1][j-2]*(i-j))%mod;      
        }
    }
    cout << dp[n][m]%mod << endl;

    return 0;
}