PU Find Median from Data Stream

addNum(1)
addNum(2)
findMedian() -> 1.5
addNum(3) 
findMedian() -> 2

struct Heap {
    int *heap;
    int top;
    int size;
    bool (*cmp)(int a, int b);
};

typedef struct {
    struct Heap *p;
    struct Heap *q;
} MedianFinder;

bool smaller(int a, int b) {
    return a < b;
}

bool bigger(int a, int b) {
    return a > b;
}

struct Heap *create(bool (*cmp)(int, int)) {
    struct Heap *res = malloc(sizeof(struct Heap));
    res->size = 1000;
    res->top = 1;
    res->heap = malloc(res->size * sizeof(int));
    res->cmp = cmp;
    return res;
}

/** initialize your data structure here. */
MedianFinder* medianFinderCreate() {
    MedianFinder *obj = malloc(sizeof(MedianFinder));
    obj->p = create(smaller);
    obj->q = create(bigger);
    return obj;
}

int pop(struct Heap *h) {
    int res = h->heap[1];
    h->heap[1] = h->heap[--h->top];
    int root = 1, child = 2;
    while (child < h->top) {
        if (child + 1 < h->top && h->cmp(h->heap[child], h->heap[child + 1])) child++;
        if (!h->cmp(h->heap[root], h->heap[child])) return res;
        int tmp = h->heap[root];
        h->heap[root] = h->heap[child];
        h->heap[child] = tmp;
        root = child;
        child = root * 2;
    }
    return res;
}

void push(struct Heap *h, int num) {
    if (h->top == h->size) {
        h->size += 1000;
        h->heap = realloc(h->heap, h->size * sizeof(int));
    }
    h->heap[h->top++] = num;
    int cur = h->top - 1, root = cur / 2;
    while (root && h->cmp(h->heap[root], h->heap[cur])) {
        int tmp = h->heap[root];
        h->heap[root] = h->heap[cur];
        h->heap[cur] = tmp;
        cur = root;
        root = cur / 2;
    }
}

void medianFinderAddNum(MedianFinder* obj, int num) {
    push(obj->p, num);
    push(obj->q, pop(obj->p));
    struct Heap *tmp = obj->p;
    obj->p = obj->q;
    obj->q = tmp;
}

double medianFinderFindMedian(MedianFinder* obj) {
    if (obj->p->top == obj->q->top) return (obj->p->heap[1] + obj->q->heap[1]) / 2.0;
    if (obj->p->top > obj->q->top) return obj->p->heap[1];
    return obj->q->heap[1];
}

void medianFinderFree(MedianFinder* obj) {
    free(obj->p->heap);
    free(obj->q->heap);
    free(obj->p);
    free(obj->q);
    free(obj);
}

/**
 * Your MedianFinder struct will be instantiated and called as such:
 * struct MedianFinder* obj = medianFinderCreate();
 * medianFinderAddNum(obj, num);
 * double param_2 = medianFinderFindMedian(obj);
 * medianFinderFree(obj);
 */