bzoj1306: [CQOI2009]match循环赛

#include<cstring>
#include<cstdio>
#include<iostream>
using namespace std;
const int f[]={3,1,0,0};
int a[9],b[9],n,ans;
inline void dfs(int x,int y){
if (b[x]>a[x]) return;
if (b[x]+(n-y+1)*3<a[x]) return;
if (x==n){ans++; return;}
if (y==n){
int t=a[x]-b[x];
if (t==2) return;
b[y]+=f[t];
dfs(x+1,x+2);
b[y]-=f[t];
}
else{
b[x]+=3; dfs(x,y+1); b[x]-=3;
b[y]+=3; dfs(x,y+1); b[y]-=3;
b[x]++; b[y]++; dfs(x,y+1); b[x]--; b[y]--;
}
}
int main(){
scanf("%d",&n);
for (int i=1;i<=n;i++) scanf("%d",&a[i]);
dfs(1,2);
printf("%d",ans);
return 0;
}