Wie ändert man die Priorität eines Wertes in einem Max-Heap?

Question

Ich schreibe einen Max-Heap, der die Priorität/Wert ändern kann. Ich habe jedoch Probleme zu verstehen, was in meinem Code falsch ist. Ich habe dies als Referenz gefolgt: ref Dies ist mein Code (Ich habe einige Funktionen verstecken, da es nicht der Fokus hier)

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); 
    } 
} 

Wenn ich die folgende Ausführung haben, ist es schlechte Ergebnisse gibt ... was ist falsch hier? Zum Beispiel ...

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); 
} 

Bitte beachte, dass ich ein Array verwenden die Indizes von HEAP_ELEM zu speichern, um die Position eines HEAP_ELEM zu wissen (was das „fu“ als Primärschlüssel hat und seine Priorität ändern. Diese meine Ausgabe:

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

ich habe meine modify_maxheap Funktion geändert und es funktioniert:

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); 
} 

der Grund dafür ist, dass wir zu blasen und Blase-down im Fall einer Änderung Garantie haben die Heap-Bedingung. Ich hoffe, dass es als Basis für jemanden dienen kann.