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优先级队列的Java ，C++ STL，堆实现

0 整理自网络

1. Java版（转）要比较的对象必须实现Comparable接口，重写compareTo 方法，Java在红自带有优先级队列的实现PriorityQueue

Queue<ToDoItem> q = new PriorityQueue<ToDoItem>();

import java.util.Collections;
import java.util.PriorityQueue;
import java.util.Queue;


public class ToDoItem implements Comparable<ToDoItem>{
    private char primary;
    private int secondary;
    private String item;
    
    public ToDoItem(char primary,int secondary,String item)
    {
        super();
        this.primary = primary;
        this.secondary = secondary;
        this.item = item;
    }

    @Override
    public int compareTo(ToDoItem o) {
        // TODO Auto-generated method stub
        
        if(this.primary > o.primary)
            return 1;
        if(this.primary == o.primary)
        {
            if(this.secondary > o.secondary)
                return 1;
            else if(this.secondary == o.secondary)
                return 0;
        }
        return -1;
    }
    
     public String toString() {  
            return Character.toString(primary) + this.secondary + " : " + this.item;  
        }
     
     public static void main(String [] args)
     {
         Queue<ToDoItem> q = new PriorityQueue<ToDoItem>();
         q.add(new ToDoItem('C', 4, "Empty trash"));
            q.add(new ToDoItem('A', 2, "Feed dog"));
            q.add(new ToDoItem('B', 7, "Feed bird"));
            q.add(new ToDoItem('C', 3, "Mow lawn"));
            q.add(new ToDoItem('A', 1, "Water lawn"));
            q.add(new ToDoItem('B', 1, "Feed cat"));
            
            while (!q.isEmpty()) {
                System.out.println(q.remove());
            }
            
            Queue<ToDoItem> q1 = new PriorityQueue<ToDoItem>(1,
                    Collections.reverseOrder());
            q1.add(new ToDoItem('C', 4, "Empty trash"));
            q1.add(new ToDoItem('A', 2, "Feed dog"));
            q1.add(new ToDoItem('B', 7, "Feed bird"));
            q1.add(new ToDoItem('C', 3, "Mow lawn"));
            q1.add(new ToDoItem('A', 1, "Water lawn"));
            q1.add(new ToDoItem('B', 1, "Feed cat"));

            while (!q1.isEmpty()) {
                System.out.println(q1.remove());
            }
            
     }
     
     

}

　　2. C++ STL 版

STL中也有自带的priority_queue 而且可以有2种比较的方式，greater和less

     priority_queue<node,vector<node>,greater<node> > queue1;
    priority_queue<node,vector<node>, less<node> > queue2;

     其中比较可以通过operator还重载

     friend bool operator > (const node &a,const node &b)
    {
        return (a.z > b.z);
    }
    friend bool operator < (const node &a,const node &b)
    {
        return (a.z < b.z);
    }

#include <iostream>
#include <vector>
#include <queue>
using namespace std;
struct node
{
    int x;
    int y;
    int z;
    friend bool operator > (const node &a,const node &b)
    {
        return (a.z > b.z);
    }
    friend bool operator < (const node &a,const node &b)
    {
        return (a.z < b.z);
    }
};



int main()
{
    priority_queue<node,vector<node>,greater<node> > queue1;
    priority_queue<node,vector<node>, less<node> > queue2;
    node n[10];
    for(int i = 0;i < 10;i ++)
    {
        n[i].x = i;
        n[i].y = 10 - i;
        n[i].z = i;
        queue1.push(n[i]);
        queue2.push(n[i]);
    }

    while(!queue1.empty())
    {
        cout << queue1.top().x << " " << queue1.top().y <<" " << queue1.top().z << endl;
        queue1.pop();
    }
    cout << endl;

    while(!queue2.empty())
    {
        cout << queue2.top().x << " " <<  queue2.top().y << " " << queue2.top().z << endl;
        queue2.pop();
    }
     cout << endl;

    return 0;
}

　　还可以通过自定义函数法，是一个仿函数

#include <iostream>
#include <queue>
#include <vector>
#include <functional>
using namespace std;
struct node
{
    int x;
    int y;
    int z;
};

struct node_greater_cmp
{
    bool operator()(const node & a,const node & b)
    {
        return a.z>b.z;
    }
};

struct node_less_cmp
{
    bool operator()(const node &a,const node &b)
    {
        return a.z < b.z;
    }
};


int main()
{
    priority_queue<node,vector<node>,node_greater_cmp > queue1;
    priority_queue<node,vector<node>,node_less_cmp > queue2;
    node n[5];

    for(int i = 0;i < 5; i ++)
    {
        n[i].x = i;
        n[i].y = 5 - i;
        n[i].z = i;
        queue1.push(n[i]);
        queue2.push(n[i]);
    }

     while(!queue1.empty())
    {
        cout << queue1.top().x << " " << queue1.top().y <<" " << queue1.top().z << endl;
        queue1.pop();
    }
    cout << endl;

    while(!queue2.empty())
    {
        cout << queue2.top().x << " " <<  queue2.top().y << " " << queue2.top().z << endl;
        queue2.pop();
    }
     cout << endl;


    return 0;
}

　　3. 自己实现，以建堆的方式实现优先级队列

#include <iostream>

using namespace std;
const int INF = 999999;
//堆调整
void maxHeapify(int *a, int i, int len)
{
    int lt = 2*i, rt = 2*i+1;
    int largest;
    if(lt <= len && a[lt] > a[i])
        largest = lt;
    else
        largest = i;
    if(rt <= len && a[rt] > a[largest])
        largest = rt;
    if(largest != i)
    {
        int temp = a[i];
        a[i] = a[largest];
        a[largest] = temp;
        maxHeapify(a, largest, len);
    }
}
//建最大堆
void buildMaxHeap(int *a,int size)
{
    for(int i = size / 2;i >= 1;i --)
    maxHeapify(a,i,size);
}
void print(int *a,int size)
{
    for(int i = 1;i <= size; i ++)
    cout << a[i] << " ";
    cout << endl;
}

int heapMaximum(int *a)
{
    return a[1];
}
//提取并返回具有最大关键字的元素
int heapExtractMax(int *a,int &heapsize)
{
    if(heapsize < 1)
          cout << "heap underflow !" << endl;

    int max = a[1];

    a[1] = a[heapsize];
    -- heapsize;

    maxHeapify(a,1,heapsize);
    return max;
}
//将a[i]增加到key，模拟优先级的提高
void heapIncreaseKey(int *a,int i,int key)
{
    if(key < a[i])
    cout << "new key is less than current key ! "  << endl;
    a[i] = key;
    while(i > 1 && a[i/2] < a[i])
    {
        int temp = a[i];
        a[i] = a[i/2];
        a[i/2] = temp;
        i /= 2;
    }

}
//插入关键字为key 的元素
void insert(int *a,int key,int &heapsize)
{
    ++heapsize;
    a[heapsize] = -INF;
    heapIncreaseKey(a,heapsize,key);
}


int main()
{
    int len,heapsize;
    int a[100] = {0, 15, 13, 9, 5, 12, 8, 7, 4, 0, 6, 2, 1};
    len = heapsize = 12;

    buildMaxHeap(a,len);
    cout << "建堆后：" << endl;
    print(a,heapsize);

    cout << "当前最大的元素：" << endl;
    cout << heapMaximum(a) << endl;

    cout << "使用heapextractmax后：" << endl;
    int maxx = heapExtractMax(a,heapsize);

    print(a,heapsize);

    cout << "再次使用heapextractmax后：" << endl;
    heapExtractMax(a,heapsize);
    print(a,heapsize);

    cout << "使用heapIncreaceKey后：" << endl;
    heapIncreaseKey(a,2,15);
     print(a,heapsize);

    cout << "使用insert插入28后：" << endl;
    insert(a,28,heapsize);
    print(a,heapsize);


    cout << "使用insert插入100后：" << endl;
    insert(a,100,heapsize);
    print(a,heapsize);

    return 0;
}