7-1 n queen problem

7-1 n queens problem

Ask for in n*n The chessboard of the grid will not attack each other n A queen . According to the rules of chess , The queen can attack the pieces on the same row, column or diagonal line .

Input format :
There are multiple sets of test data , Processing to the end of the file . For each group of tests , Enter the size of the chessboard n（1<n<12）.

Output format :
For each group of tests , Output the number of schemes that meet the requirements .

sample input :

4

sample output :

2

Code ：

#include <iostream>
#include<stdio.h>
#include<math.h>
using namespace std;
int n,a[200],plan;
void dfs(int x){
    
    if(x>n){
    
        plan++;
        return;
    }
    for(int i=1;i<=n;i++){
    
        a[x]=i;
        int flag=0;
        for(int j=1;j<=x-1;j++){
    
            if(a[x] == a[j] || fabs(x-j)==fabs(a[x]-a[j])){
    
                flag=1;
                break;
            }
        }
        if(flag==0)
            dfs(x+1);
    }
}
int main()
{
    
    while(scanf("%d",&n)!=EOF){
    
        plan=0;
        for(int i=1;i<20;i++)
            a[i]=0;
         dfs(1);
         cout<<plan<<endl;
    }
    return 0;
}

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