bzoj1925: [Sdoi2010]地精部落

orz神犇

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
using namespace std;

int f[2][5100];
int main()
{
    int n,mod;
    scanf("%d%d",&n,&mod);
    if(n==1){printf("1\n");return 0;}
    
    int now=1;
    memset(f,0,sizeof(f));f[now][1]=1%mod;
    for(int i=2;i<=n+1;i++)
    {
        now^=1;
        for(int j=1;j<=i;j++)
            f[now][j]=(f[now][j-1]+f[now^1][i-j+1])%mod;
    }
    printf("%d\n",f[now][n+1]*2%mod);
    
    return 0;
}