USACO：Checker Challenge

/*
ID: Jang Lawrence
PROG: checker
LANG: C++
*/
#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;
bool is[14];
bool is2[30],is3[30];
int n,ans;
int c[14];
bool f(int &x,int &y)
{
if(is[y]) return false;
int k=y-(x-1)+1+n;
if(is2[x+y]||is3[k]) return false;
return 1;
}
void dfs(int row)
{
if(row==n+1)
{
ans++;
if(ans<=3)
{
for(int i=1;i<n;++i)
printf("%d ",c[i]);
printf("%d\n",c
);
}
return ;
}
for(int i=1;i<=n;++i)
if(f(row,i))
{c[row]=i;is[i]=1;is2[row+i]=1;
int k=i-(row-1)+1+n;
is3[k]=1;
dfs(row+1);is[i]=0;is2[row+i]=0;
is3[k]=0;}
}
int main()
{
#ifndef  DEBUG
freopen("checker.in","r",stdin);
freopen("checker.out","w",stdout);
#endif
scanf("%d",&n);
dfs(1);
printf("%d\n",ans);
return 0;
}