[BZOJ1925][SDOI2010]地精部落

 1 #include<cstdio>
 2 #include<queue>
 3 #include<iostream>
 4 #include<cstring>
 5 using namespace std;
 6 inline int read(){
 7     int ans=0,f=1;char chr=getchar();
 8     while(!isdigit(chr)){if(chr=='-') f=-1;chr=getchar();}
 9     while(isdigit(chr)){ans=(ans<<3)+(ans<<1)+chr-48;chr=getchar();}
10     return ans*f;
11 }int n,ha,dp[2][4201],ans;
12 int main(){
13     n=read(),ha=read();
14     dp[0][2]=1;
15     for(int i=3;i<=n;i++)
16         for(int j=2;j<=i;j++)
17             dp[i&1][j]=(dp[i&1][j-1]+dp[(i-1)&1][i-j+1])%ha;
18     for(int i=2;i<=n;i++) ans=(ans+dp[n&1][i])%ha;
19     cout<<(ans<<1)%ha;
20     return 0;
21 }