How to modify the priority of a value in a max-heap?

Question

I am writing a max-heap, which can change the priority/value. However, I have problems to understand what is wrong in my code. I have followed this as reference: ref This is my code (I have hide some functions since it not the focus here)

static void swap(MAX_HEAP *heap, int i, int j);
static void swim(MAX_HEAP *heap, int k);
static void sink(MAX_HEAP *heap, int k);

void swap(MAX_HEAP *heap, int i, int j) {
    HEAP_ELEM s;
    int k;

    s = heap->binary_heap[i];
    k = heap->keys[s.fu];

    heap->binary_heap[i] = heap->binary_heap[j];
    heap->keys[k] = heap->keys[heap->binary_heap[j].fu];

    heap->keys[heap->binary_heap[j].fu] = k;
    heap->binary_heap[j] = s;
}

void swim(MAX_HEAP *heap, int k) {
    int m;
    m = k / 2.0;
    while (k > 1 && heap->binary_heap[m].priority < heap->binary_heap[k].priority) {
        swap(heap, k, m);
        k = m;
        m = k / 2.0;
    }
}

void sink(MAX_HEAP *heap, int k) {
    int j;
    while (2 * k <= heap->n) {
        j = 2 * k;
        if (j < heap->n && heap->binary_heap[j].priority < heap->binary_heap[j + 1].priority)
            j++;
        if (!(heap->binary_heap[k].priority < heap->binary_heap[j].priority))
            break;
        swap(heap, k, j);
        k = j;
    }
}

MAX_HEAP *create_maxheap(int capacity) {
    int i;

    MAX_HEAP *ret;
    ret = (MAX_HEAP*) malloc(sizeof (MAX_HEAP));
    ret->n = 0;
    ret->binary_heap = (HEAP_ELEM*) malloc(sizeof (HEAP_ELEM) * (capacity + 1));
    ret->binary_heap[0].fu = 0;
    ret->binary_heap[0].priority = 0;
    ret->max = capacity;

    ret->keys = (int*) malloc(sizeof (int) * (capacity + 1));
    for (i = 0; i <= capacity + 1; i++) {
        ret->keys[i] = -1;
    }

    return ret;
}

HEAP_ELEM get_maxheap(MAX_HEAP *heap) {
    HEAP_ELEM ret;
    if (heap->n == 0) {
        return;
    }
    ret = heap->binary_heap[1];

    heap->keys[ret.fu] = -1;

    swap(heap, 1, heap->n);
    heap->n--;
    sink(heap, 1);

    return ret;
}

void insert_maxheap(MAX_HEAP *heap, int fu, int p) {
    if (heap->n + 1 >= heap->max) {
        int i;
        heap->max *= 2;
        heap->keys = (int*) realloc(heap->keys, sizeof (int) * (heap->max + 1));
        heap->binary_heap = (HEAP_ELEM*) realloc(heap->binary_heap, sizeof (HEAP_ELEM) * (heap->max + 1));
        for (i = heap->n+1; i < heap->max + 1; i++) {
            heap->keys[i] = -1;
        }
    }

    heap->n++;
    heap->binary_heap[heap->n].fu = fu;
    heap->binary_heap[heap->n].priority = p;
    heap->keys[fu] = heap->n;
    swim(heap, heap->n);
}

void modify_maxheap(MAX_HEAP *heap, int fu, int p) {
    int i;
    i = heap->keys[fu];
    int old;

    if (i == -1) {
        insert_maxheap(heap, fu, p);
        return;
    }

    old = heap->binary_heap[i].priority;

    heap->binary_heap[i].fu = fu;
    heap->binary_heap[i].priority = p;
    heap->keys[fu] = i;

    if (old < p) {
        /* we need to bubble up*/
        swim(heap, i);
    } else if (old > p) {
        //we need to bubble down
        sink(heap, i);
    }
}

When I have the following execution, it gives bad results... what is wrong here? For instance...

int main(int argc, char** argv) {
    MAX_HEAP *heap, *heap2;
    HEAP_ELEM he;
    heap = create_maxheap(3);

    modify_maxheap(heap, 1, 7);
    modify_maxheap(heap, 2, 10);
    modify_maxheap(heap, 3, 78);
    modify_maxheap(heap, 4, 3);
    modify_maxheap(heap, 5, 45);

    printf("heap 1\n\n");
    while(heap->n > 0) {
        he = get_maxheap(heap);
        printf("..fu: %d; value: %d\n", he.fu, he.priority);
    }
    printf("max size of heap1: %d\n", heap->max);
    printf("\n\n");

    heap2 = create_maxheap(10);

    modify_maxheap(heap2, 3, 90);
    modify_maxheap(heap2, 1, 7);    
    modify_maxheap(heap2, 2, 10);
    modify_maxheap(heap2, 3, 9);
    modify_maxheap(heap2, 3, 92);
    modify_maxheap(heap2, 4, 3);
    modify_maxheap(heap2, 3, 90);
    modify_maxheap(heap2, 1, 99);
    modify_maxheap(heap2, 5, 45);
    modify_maxheap(heap2, 1, 89);

    printf("heap 2\n\n");
     while(heap2->n > 0) {
        he = get_maxheap(heap2);
        printf("fu: %d; value: %d\n", he.fu, he.priority);
    }


    return (EXIT_SUCCESS);
}

Note that I am using an array to store the indices of HEAP_ELEM in order to know the position of a HEAP_ELEM (which has as primary key the "fu" and change its priority. This is my output:

heap 1

..fu: 3; value: 78
..fu: 5; value: 45
..fu: 2; value: 10
..fu: 1; value: 7
..fu: 4; value: 3
max size of heap1: 6


heap 2

fu: 1; value: 99
fu: 3; value: 90
fu: 1; value: 89
fu: 5; value: 45
fu: 4; value: 3

Answer 1

I have changed my modify_maxheap function and it worked:

void modify_maxheap(MAX_HEAP *heap, int fu, int p) {
    int i;
    i = heap->keys[fu];

    if (i == -1) {
        insert_maxheap(heap, fu, p);
        return;
    }    

    heap->binary_heap[i].priority = p;
    swim(heap, i);
    sink(heap, i);
}

The reason is that we have to bubble-up and bubble-down in case of any modification to guarantee the heap condition. I hope it can serve as base for someone.