最大堆

      根据《算法导论》中介绍的算法实现。

      

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
typedef struct priority_queue_tag {
    int heap_size;
    int *array;
} priority_queue;

int parent(int i)
{
    return (i - 1) / 2;
}

int left_child(int i)
{
    return i * 2 + 1;
}

int right_child(int i)
{
    return i * 2 + 2;
}

void swap(int *a, int *b) 
{
    if(a == NULL|| b == NULL || a==b)
        return;
    int t = *a; 
    *a = *b; 
    *b = t;
}

void heapify(priority_queue *pq, int i)
{
    int left = left_child(i);
    int right = right_child(i);
    int largest = i;
    if (left < pq->heap_size
            && pq->array[largest] < pq->array[left]) {
        largest = left;
    }
    if (right < pq->heap_size
            && pq->array[largest] < pq->array[right]) {
        largest = right;
    }
    if (largest != i) {
        swap(&pq->array[i], &pq->array[largest]);
        heapify(pq, largest);
    }
}

void fix_up(priority_queue *pq, int i)
{
    while (i > 0 && pq->array[parent(i)] < pq->array[i]) {
        swap(&pq->array[parent(i)], &pq->array[i]);
        i = parent(i);
    }
}

priority_queue *priority_queue_create(int n)
{
    priority_queue *pq = (priority_queue *)malloc(sizeof(priority_queue));
    pq->array = (int *)malloc(sizeof(void *) * n);
    pq->heap_size = 0;
    return pq;
}

int priority_queue_top(priority_queue* pq)
{
    return pq->array[0];
}
/*去掉并返回堆的第一个元素 */
int priority_queue_extract_top(priority_queue* pq)
{
    int i = pq->heap_size - 1;
    swap(&pq->array[0], &pq->array[i]);
    --pq->heap_size;
    heapify(pq, 0);
    return pq->array[i];
}

/*把元素key插入队列 */
void priority_queue_insert(priority_queue *pq, int key)
{
    int i = pq->heap_size;
    pq->array[i] = key;
    ++pq->heap_size;
    fix_up(pq, i);
}

bool priority_queue_is_empty(priority_queue *pq)
{
    return pq->heap_size == 0;
}

void priority_queue_destroy(priority_queue *pq)
{
    free(pq->array);
    free(pq);
}

int main()
{
    priority_queue *pq = priority_queue_create(10);
    for (int i = 0; i < 10; i++) {
        priority_queue_insert(pq, i);
        }
    printf("最大堆结果:
");
    while (!priority_queue_is_empty(pq)) {
        int p = priority_queue_extract_top(pq);
        printf("%d ", p);
    }
    printf("
");
    priority_queue_destroy(pq);
    return 0;
}