N-Queens.c

// WAP to implement general backtracking strategy to solve 8-queens and take n as user input
#include <stdio.h>
#include <stdbool.h>


#define N 8


void printSolution(int board[N][N]) {
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            printf("%2d ", board[i][j]);
        }
        printf("\n");
    }
}


bool isSafe(int board[N][N], int row, int col) {
    // Check the row on the left side
    for (int i = 0; i < col; i++) {
        if (board[row][i])
            return false;
    }


    // Check upper diagonal on the left side
    for (int i = row, j = col; i >= 0 && j >= 0; i--, j--) {
        if (board[i][j])
            return false;
    }


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


    return true;
}


bool solveNQueensUtil(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 (solveNQueensUtil(board, col + 1))
                return true;
            board[i][col] = 0; // Backtrack
        }
    }


    return false;
}


bool solveNQueens() {
    int board[N][N] = {0};


    if (solveNQueensUtil(board, 0) == false) {
        printf("Solution does not exist\n");
        return false;
    }


    printSolution(board);
    return true;
}


int main() {
    solveNQueens();
    return 0;
}