优先队列

https://blog.csdn.net/Sungree/article/details/100834974

注意：因为是数组表示（有值的区域里没有空缺），所以这个二叉树是完全二叉树

大顶堆：

C语言代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define Type int

typedef struct HeapStruct{
    int capacity;
    int size;
    Type* eles;
}PriorityQueue;

PriorityQueue* Init(int max_size){
    PriorityQueue* pq;
    if(max_size <= 0){
        printf("max_size is illegal !\n");
        return NULL;
    }
    pq = malloc(sizeof(PriorityQueue));
    if(pq == NULL){
        printf("malloc failed !\n");
        return NULL;
    }
    pq -> eles = malloc((max_size + 1)*sizeof(Type));
    if(pq -> eles == NULL){
        printf("eles malloc failed !\n");
        free(pq);  //如果eles没有malloc成功，记得把pq给释放掉 
        return NULL;
    }
    memset(pq -> eles,0,(max_size + 1)*sizeof(Type));//记得要初始化 
    pq -> capacity = max_size;
    pq -> size = 0;
    return pq;
}

int is_Empty(PriorityQueue* pq){ //为什么不用bool？因为C语言有些编译器不能用bool 
    if(pq == NULL)  return 0;
    if(pq -> size == 0)  return 1;
    return 0;
}

int is_Full(PriorityQueue* pq){
    if(pq == NULL){
      printf("Queue is empty !\n");
      return 0;
    } 
    if(pq -> capacity == pq -> size)  return 1;
    return 0;
}

int push(Type value,PriorityQueue* pq){
    if(is_Full(pq)){
        printf("Queue is full !\n");
        return 0;
    }
    printf("push %d\n", value);
    int i = pq -> size + 1;
    for(;i > 1;i /= 2){ //为什么i != 1?因为当i == 1时，i/2 == 0 就越界了 
        if(value > pq -> eles[i/2])
          pq -> eles[i] = pq -> eles[i/2];
        else
          break;
    }
    /*int i;
    for(i = pq->size+1; value > pq->eles[i/2] && i>1; i/=2){
        pq->eles[i] = pq->eles[i/2];
    } */
    pq -> eles[i] = value;//不要忘了把空穴补上 
    pq -> size ++;
    return 1;
}

int find_max(PriorityQueue* pq,Type* max){
    if(is_Empty(pq)){
        printf("Queue is empty !\n");
        return 0;
    }
    *max = pq -> eles[1];
    return 1;
}

int pop(PriorityQueue* pq,Type* max){
    if(is_Empty(pq)){
        printf("Queue is empty !\n");
        return 0;
    }
    *max = pq -> eles[1];
    printf("Pop %d\n", pq->eles[1]);
    Type last = pq -> eles[pq -> size];
    pq -> size --;
    if(pq -> size == 0){
        pq -> eles[1] = 0;
        return 1;
    }
    int i = 1,maxchild;
    for(;2*i <= pq -> size;i = maxchild){    //这里重新调整优先队列和push是一样的，只是push是从下往上，这里是从在最上面往下补
        maxchild = 2*i;
        if(maxchild < pq -> size)
         if(pq -> eles[maxchild] < pq -> eles[maxchild + 1])
          maxchild = maxchild + 1;
        if(last < pq -> eles[maxchild])
         pq -> eles[i] = pq -> eles[maxchild];
        else
         break;
    }
    pq -> eles[i] = last;
    return 1;
}

int destroy(PriorityQueue* pq){
    if(pq == NULL)  return 0;
    free(pq -> eles);
    pq -> eles = NULL;
    free(pq);
    pq = NULL;
    printf("destroy success !\n");
    return 1;
}

int main(int argc, char *argv[]) {
    //创建容量为6的优先队列 
    PriorityQueue *pq = Init(6); //init在定义时，定义为指针，因此其返回值是个指针，直接复制给pq 
    
    int arr[]={3,4,7,5,8,2,9,10} ;
    int i = 0;
    
    //试图插入多于6个的元素，最后两个元素将无法插入 
    for(i = 0; i<8; i++){
        push(arr[i], pq);
    } 
    
    //遍历队列内容
    printf("the value of pq are: ") ;
    for(i=0; i<pq->size; i++){
        printf("%d ", pq->eles[i+1]); 
    }
    printf("\n");
    printf("pq size is %d\n", pq->size);
    
    Type max;
    int size = pq->size;
    //每次从堆顶取元素
    for(i=0; i<size; i++){
        if(find_max(pq, &max)){
            printf("the max is %d\n", max);
            pop(pq, &max);
        }    
    }
    printf("new size is %d\n", pq->size) ;
    
    //销毁队列 
    destroy(pq);

    return 0;
}