优先级队列

#include <iostream>
using namespace std;

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

int left(int i)
{
    return 2*i;
}

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

void exchange(int &a,int &b)
{
    int temp;
    temp=a;
    a=b;
    b=temp;
}

//但就算法来看，heap_size（堆的大小）设为全局变量也许会好一些
void max_heapify(int *a,int i,int heap_size)
{
    int l=left(i);
    int r=right(i);
    int largest;
    if (l<=heap_size&&a[l]>a[i])
    {
        largest=l;
    }
    else
    {
        largest=i;
    }
    if (r<=heap_size&&a[r]>a[largest])
    {
        largest=r;
    }
    if (largest!=i)
    {
        exchange(a[i],a[largest]);
        max_heapify(a,largest,heap_size);
    }

}

void build_max_heap(int *a,int heap_size)
{
    for (int i=heap_size/2;i>=0;i--)
    {
        max_heapify(a,i,heap_size);
    }
}

int heap_maximum(int *a)
{
    return a[0];
}

int heap_extract_max(int *a,int heap_size)
{
    if (heap_size<0)
    {
        cout<<"heap_underflow"<<endl;
        return 0;
    }

    int Max=a[0];
    a[0]=a[heap_size];
    heap_size=heap_size-1;
    max_heapify(a,0,heap_size);
    return Max;
}

void heap_increase_key(int *a,int i,int key)
{
    if (key<a[i])
    {
        cout<<"new key is small than current key"<<endl;
        return;
    }

    a[i]=key;
    while (i>0&&a[parent(i)]<a[i])
    {
        exchange(a[i],a[parent(i)]);
        i=parent(i);
    }
}

void max_heap_insert(int *a,int key,int heap_size)        
{
    heap_size=heap_size+1;
    a=(int*)realloc(a,sizeof(int)*(heap_size+1));
    a[heap_size]=-10000;
    heap_increase_key(a,heap_size,key);
}

int main()
{
    int b[]={4,1,3,2,16,30,10,14};
    int *a;
    int heap_size=sizeof(b)/sizeof(int)-1;
    a=(int*)malloc(sizeof(int)*(heap_size+1));
    memcpy(a,b,sizeof(int)*(heap_size+1));

    build_max_heap(a,heap_size);
    max_heap_insert(a,11,heap_size);

    for (int i=0;i<=heap_size+1;i++)
        cout<<a[i]<<"";

    cout<<endl;
    cout<<heap_maximum(a)<<endl;
    cout<<heap_extract_max(a,heap_size+1)<<endl;

    for (int i=0;i<=heap_size;i++)
        cout<<a[i]<<"";
    
    cout<<endl;
    system("pause");
    free(a);
    return 0;

}