heapq.c

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

    typedef struct {
        int priority;
        int value;
    } Item;

    typedef struct {
        Item* heap;
        int capacity;
        int size;
    } HeapQueue;

    HeapQueue* hq_create(int capacity) {
        HeapQueue* hq = (HeapQueue*)malloc(sizeof(HeapQueue));
        hq->capacity = capacity;
        hq->size = 0;
        hq->heap = (Item*)malloc(capacity * sizeof(Item));
        return hq;
    }

    void hq_destroy(HeapQueue* hq) {
        free(hq->heap);
        free(hq);
    }

    void hq_enqueue(HeapQueue* hq, int priority, int value) {
        if (hq->size == hq->capacity) {
            fprintf(stderr, "HeapQueue is full. Cannot enqueue.\n");
            return;
        }

        Item item = { priority, value };
        int i = hq->size++;
        int parent = (i - 1) / 2;

        while (i > 0 && hq->heap[parent].priority > item.priority) {
            hq->heap[i] = hq->heap[parent];
            i = parent;
            parent = (i - 1) / 2;
        }

        hq->heap[i] = item;
    }

    Item hq_dequeue(HeapQueue* hq) {
        if (hq->size == 0) {
            fprintf(stderr, "HeapQueue is empty. Cannot dequeue.\n");
            return (Item){0, 0};
        }

        Item root = hq->heap[0];
        Item last = hq->heap[--hq->size];
        int i = 0;
        int child = 1;

        while (child < hq->size) {
            if (child + 1 < hq->size && hq->heap[child + 1].priority < hq->heap[child].priority) {
                child++;
            }

            if (last.priority <= hq->heap[child].priority) {
                break;
            }

            hq->heap[i] = hq->heap[child];
            i = child;
            child = 2 * i + 1;
        }

        hq->heap[i] = last;
        return root;
    }

    int main() {
        HeapQueue* hq = hq_create(10);

        hq_enqueue(hq, 2, 20);
        hq_enqueue(hq, 4, 40);
        hq_enqueue(hq, 1, 10);
        hq_enqueue(hq, 3, 30);

        while (hq->size > 0) {
            Item item = hq_dequeue(hq);
            printf("Priority: %d, Value: %d\n", item.priority, item.value);
        }

        hq_destroy(hq);
        return 0;
    }