6a_NQueens.cpp

#define N 4
#include <iostream>
#include <stdbool.h>
#include <stdio.h>
using namespace std;

void printSolution(int board[N][N])
{
    int i,j;
    for(i=0;i<N;i++)
    {
        for(j=0;j<N;j++)
            cout<<board[i][j];
        cout<<"\n";
    }
}

bool isSafe(int board[N][N],int row,int col)
{
    int i,j;
    for(i=0;i<col;i++)
        if(board[row][i])
            return false;
    for(i=row,j=col;i>=0 && j>=0;i--,j--)
        if(board[i][j])
            return false;
    for(i=row,j=col;j>=0 && i<N;i++,j--)
        if(board[i][j])
            return false;
    return true;
}

bool solveNQUtil(int board[N][N],int col)
{

    if(col>=N)
        return true;
    for(int i=0;i<N;i++)
    {
        if(isSafe(board,i,col))
        {
            board[i][col]=1;
            if(solveNQUtil(board,col+1))
                return true;
            board[i][col]=0;
        }
    }
    return false;
}

bool solveNQ()
{
    int board[N][N]={{0,0,0,0},
                     {0,0,0,0},
                     {0,0,0,0},
                     {0,0,0,0}};
    if(solveNQUtil(board,0)==false)
    {
        cout<<"Solution does not exist.";
        return false;
    }
    printSolution(board);
    return true;
}
int main()
{
    solveNQ();
    return 0;
}