chess_queens.c

#include <stdio.h>
#include <stdlib.h>

int n;
int *rows = NULL;

// Initialize global arrays
void init_glob (int n)
{
    int i = 0;
    rows = (int *)malloc(n * sizeof(int));
    for (; i < n; i++) {
        rows[i] = -1;
    }

}

// Free global arrays
void free_glob ()
{
    free(rows);
}

void dfs (int seed)
{
    static int deepth = 0;
    int i = 0;
    int j = 0;

    rows[deepth] = seed;
    deepth += 1;

    if (deepth == n) {
        for (i = 0; i < n; i++) {
            printf("%c%d ", i + 'a', rows[i] + 1);
        }
        printf("\n");
    } else {

        int *temp = (int *)calloc(n, sizeof(int));

        for (i = 0; i < deepth; i++) {
            temp[rows[i]] = 1;
            j = deepth - i;
            if (rows[i] + j < n)
                temp[rows[i] + j] = 1;
            if (rows[i] - j >= 0)
                temp[rows[i] - j] = 1;
        }

        for (i = 0; i < n; i++)
            if (!temp[i])
                dfs(i);

        free(temp);
    }

    deepth -= 1;
    rows[deepth] = -1;
}

int main(void)
{
    int i = 0;
    scanf("%d", &n);
    init_glob (n);
    for (i = 0; i < n; i++) {
        dfs(i);
    }
    free_glob();
    return 0;
}