n_queen.c

#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
int n;
void printSolution(int board[n][n]) 
{
    for (int i = 0; i < n; i++) 
    {
        for (int j = 0; j < n; j++) 
            printf("%d ", board[i][j]);
        printf("\n");
    }
}

bool isSafe(int board[n][n], int row, int col) 
{
    int i, j;

    // check row
    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;
}
bool solveNQueen(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 (solveNQueen(board, col + 1)) 
                return true;
                
            board[i][col] = 0; // backtrack
        }
    }

    return false;
}
void main()
{
    printf("Enter the value of N for a N X N chessboard: ");
    scanf("%d",&n);
    if(n==2)
    {
        printf("not possible.");
        exit(1);
    }
    int board[n][n];
    for (int i = 0; i < n; i++) 
        for (int j = 0; j < n; j++) 
            board[i][j] = 0;
    if (solveNQueen(board, 0) == false) 
        printf("Solution does not exist");
    
    else {
        printf("Solution:\n");
        printSolution(board);
        printf("The number 1 decipts the placement of the Queens.");
    }
}