TheAlgorithms-C-Plus-Plus/Backtracking/N Queens.cpp

#include<iostream>
#define N 4
using namespace std;

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

bool isSafe(int board[N][N], int row, int col)
{
    int i, j;
 
    /* Check this row on left side */
    for (i = 0; i < col; i++)
        if (board[row][i])
            return false;
 
    /* Check upper diagonal on left side */
    for (i=row, j=col; i>=0 && j>=0; i--, j--)
        if (board[i][j])
            return false;
 
    /* Check lower diagonal on left side */
    for (i=row, j=col; j>=0 && i<N; i++, j--)
        if (board[i][j])
            return false;
 
    return true;
}
 

void solveNQ(int board[N][N], int col)
{
    
    if (col >= N){
        printSolution(board);
        return;
    }
 
    /* Consider this column and try placing
       this queen in all rows one by one */
    for (int i = 0; i < N; i++)
    {
        /* Check if queen can be placed on
          board[i][col] */
        if ( isSafe(board, i, col) )
        {
            /* Place this queen in board[i][col] */
//            cout<<"\n"<<col<<"can place"<<i;
            board[i][col] = 1;
 
            /* recur to place rest of the queens */
            solveNQ(board, col + 1);
                

            board[i][col] = 0; // BACKTRACK
        }
    }
 
}
 
 
int main()
{
    
   int board[N][N] = { {0, 0, 0, 0},
       {0, 0, 0, 0},
       {0, 0, 0, 0},
       {0, 0, 0, 0}
   };
   
	solveNQ(board, 0);
    return 0;
}