Submission #59590

#	Time	Username	Problem	Language	Result	Execution time	Memory
59590		theknife2001	Tents (JOI18_tents)	C++17	100 / 100	1047 ms	71688 KiB

tents

#include <bits/stdc++.h>

using namespace std;
const int N=3005;
long long dp[N][N];
int n,m;
long long mod=1e9+7;

long long bt(int i, int j)
{
    if(i==n)
    {
        if(j==m)
            return 0;
        return 1;
    }
    if(dp[i][j]!=-1)
        return dp[i][j];
    long long x=bt(i+1,j);
    x%=mod;
    if(j)
        x+=bt(i+1,j-1)*4*j;
    x%=mod;
    if(j&&i+2<=n)
        x+=bt(i+2,j-1)*j*(n-i-1);
    x%=mod;
    if(j>1)
        x+=((bt(i+1,j-2)*j*(j-1))/2)%mod;
    x%=mod;

    dp[i][j]=x;
    return x;
}


int main()
{
    cin>>n>>m;
    memset(dp,-1,sizeof dp);
    cout<<bt(0,m)<<endl;
    return 0;
}

• Subtask 1: 48 / 48
• Subtask 2: 52 / 52