18.2_n_queen.cpp

#include<iostream>
using namespace std;

bool isSafe(int** arr , int x, int y, int n){
    for (int row=0; row<x; row++)
    {
        if (arr[row][y] == 1){
            return false;
        }  
    }
    // for diagonal wise check
    int row=x;
    int col=y;
    while(row>=0 && col>=0){
        if(arr[row][col]==1){
            return false;
        }
        row--;
        col--;
    }

    row=x;
    col=y;
    while(row>=0 && col<=n){
        if(arr[row][col]==1){
            return false;
        }
        row--;
        col++;
    }
    return true;
}

bool nQueen(int** arr, int x, int n) // we did'nt take int y or col count because if we put queen in row then we will go to next row
{
   if (x>=n){
    return true;
   }

   for(int col=0; col<n; col++){
    if(isSafe(arr,x,col,n)){
        arr[x][col]=1;

        if(nQueen(arr, x+1,n)) //check for next row to put queen
        {
            return true;
        }

        arr[x][col] = 0; //backtracking
    }
   }
   return false;
}

int main(){
    int n;
    cin>>n;

    int** arr = new int*[n];
    for(int i=0; i<n; i++){
        arr[i] = new int[n];
        for(int j=0; j<n; j++){
            arr[i][j]=0;
        }
    }
    if(nQueen(arr,0,n)){
        for(int i=0; i<n; i++)
        {
        for(int j=0; j<n; j++)
        {
            cout<<arr[i][j]<<" ";
        }
        cout<<endl;
        }   
    }
      return 0;
}