two-stack-queue.c

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

// tos_curr is piled with shit
// tos_other is always empty (what a waste)
int *tos_curr, n_curr, *tos_other, n_other;

void stack_push(int **tos, int *n, int k) {
    **tos = k;
    *tos += 1;
    *n += 1;
}

int *stack_pop(int **tos, int *n) {
    if (*n > 0) {
        *tos -= 1;
        *n -= 1;
        return *tos;
    } else {
        return NULL;
    }
}

void stack_ptr_swap(int **tos1, int *n1, int **tos2, int *n2) {
    int *tos3 = *tos2;
    *tos2 = *tos1;
    *tos1 = tos3;

    int n3 = *n1;
    *n1 = *n2;
    *n2 = n3;
}

void stack_invert() {
   int *k = stack_pop(&tos_curr, &n_curr);

    if (NULL == k) {
        return;
    }

    while (k != NULL) {
        stack_push(&tos_other, &n_other, *k);
        k = stack_pop(&tos_curr, &n_curr);
    }

    stack_ptr_swap(&tos_curr, &n_curr, &tos_other, &n_other);
}

void queue_put(int k) {
    stack_push(&tos_curr, &n_curr, k);
}

int *queue_get() {
    stack_invert();
    int *k = stack_pop(&tos_curr, &n_curr);
    stack_invert();

    return k;
}

void queue_init() {
    tos_curr = calloc(10000, sizeof *tos_curr);
    tos_other = calloc(10000, sizeof *tos_other);
}

void main() {
    queue_init();

    queue_put(1);
    queue_put(2);
    queue_put(3);
    queue_put(4);
    queue_put(5);

    printf("%d\n", *queue_get());
    printf("%d\n", *queue_get());

    queue_put(6);
    queue_put(7);

    printf("%d\n", *queue_get());
    printf("%d\n", *queue_get());
    printf("%d\n", *queue_get());

    queue_put(8);

    printf("%d\n", *queue_get());
    printf("%d\n", *queue_get());
    printf("%d\n", *queue_get());

    printf("%p\n", queue_get());
}