N皇后

#include<stdio.h>
#include<stdlib.h>
int p[20],a[50],b[50],c[50],ans,n;
 
void dfs(intx){
     inti,j,k;
     if(x==n+1){
         ans++;
         return;
     }        
     for(i=1;i<=n;i++)
         if(a[i]+b[x+i]+c[x-i+20]==0){
             p[x]=i;
             a[i]=1;  b[x+i]=1;  c[x-i+20]=1;
             dfs(x+1);
             a[i]=0;  b[x+i]=0;  c[x-i+20]=0;                        
         }
}
int main(){
    int i,j,k,m;
    scanf("%d",&n);
    dfs(1);
    printf("%d
",ans);
    return0;    
}