NQueens.c

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#define X 99
// To reset the board and remove queens.
void reset(int *board, int dim) {
    int i;
    for(i = 0;i<dim;i++) {
	board[i] = X;
    }
}
void printBoard(int *board, int dim) {
    int i, j;
    for(i = 0;i<dim;i++) {
	for(j = 0;j<dim;j++) {
	    if(board[i] == j) {
		printf("Q   ");
	    }
	    else {
		printf("X   ");
	    }
	}
	puts("");
    }
    puts("");
}
int *initBoard(int dim) {
    int i, *board;
    board = (int *) malloc(dim*sizeof(int));
    reset(board, dim);
    return board;
}
// To check conflicts in columns and diagonals.
int checkConflict(int *board, int dim, int curRow, int curCol) {
    int i;
    for(i = 0;i<curCol;i++) {
	if(board[i] == curRow) {
	    return 1;
	}
	else if(abs(board[i] - curRow) == abs(i - curCol)) {
	    return 1;
	}
    }
    return 0;
}
int backtrack(int *board, int dim, int curCol) {
    int i, found = 0;
    // If solution is found.
    if(curCol == dim) {
	printBoard(board, dim);
	return 1;
    }
    for(i = 0;i<dim;) {
	// Check if solution is possible in ith row.
	if(checkConflict(board, dim, i, curCol)) {
	    i++;
	    continue;
	}
	else {
	    board[curCol] = i;
	    // Check solution in next column.
	    if(backtrack(board, dim, curCol + 1)) {
		found = 1;
	    }
	}
	if(curCol == 0) {
	    reset(board, dim);
	}
	i++;
    }
    return found;
}
int main() {
    int dim, *board, i;
    printf("Enter the dim : ");
    scanf("%d", &dim);
    board = initBoard(dim);
    if(!backtrack(board, dim, 0)) {
	puts("No solution found !");
    }
    free(board);
}