优先级队列

题目：优先级队列（封装堆）

注：由于大堆与小堆的实现大同小异，只需要修改大于或小于号；所以为了代码复用，本人使用了模板参数及模板的模板参数

模板的模板参数：为了引入仿函数即函数对象；此处不多介绍仿函数，它只是一个函数对象；一个类型；如下：

类型GreaterCompare与类型LessCompare：他们的内部都只是重载了();

template<class T>
struct GreaterCompare
{
bool operator()(const T& leftChild, const T& rightChild)
{
return leftChild > rightChild;
}
};

template<class T>
struct LessCompare
{
bool operator()(const T& leftChild, const T& rightChild)
{
return leftChild < rightChild;
}
};

堆的实现代码如下：

#pragma once#include<iostream>using namespace std;#include<vector>//仿函数（函数对象）template<class T>struct GreaterCompare{bool operator()(const T& leftChild, const T& rightChild){return leftChild > rightChild;}};template<class T>struct LessCompare{bool operator()(const T& leftChild, const T& rightChild){return leftChild < rightChild;}};//模板类型的模板形参template<class T,template<class> class Compare = GreaterCompare> //缺省参数class Heap{public:Heap(){}Heap(const T* arr,int len){if (arr == NULL || len <= 0)return;for (int i = 0; i < len; ++i){_heapArr.push_back(arr[i]);}//建堆：找第一个非叶子结点的父亲，然后向下调整for (int i = len - 1; i >= 0; --i){int root = (i - 1) / 2;_AdjustDown(root);}}//末尾增加一个结点后，向上调整void Push(const T& x){_heapArr.push_back(x);_AdjustUp(_heapArr.size() - 1);}//删除一个结点时，先将堆顶数据与末尾数据交换，然后删除末尾数据，最后向下调整void Pop(){swap(_heapArr[0], _heapArr[_heapArr.size() - 1]);_heapArr.pop_back();_AdjustDown(0);}T& Size(){return _heapArr.size();}bool Empty(){return _heapArr.empty();}T& Top(){return _heapArr[0];}void Print(){for (int i = 0; i < (int)_heapArr.size(); ++i){cout << _heapArr[i] << " ";}cout << endl;}~Heap(){}protected://向下调整void _AdjustDown(int root){Compare<T> com;int child = root * 2 + 1;while (child < (int)_heapArr.size()){if (child + 1 < (int)_heapArr.size() && com(_heapArr[child + 1], _heapArr[child])){++child;}if (com(_heapArr[child], _heapArr[root])){swap(_heapArr[child], _heapArr[root]);root = child;child = root * 2 + 1;}else{break;}}}//向上调整void _AdjustUp(int child){Compare<T> com;int root = (child - 1) / 2;while (child > 0){if (com(_heapArr[child], _heapArr[root])){swap(_heapArr[child], _heapArr[root]);child = root;root = (child - 1) / 2;}else{break;}}}private:vector<T> _heapArr;};//测试用例void TestHeap(){int arr[10] = { 10, 11, 13, 12, 16, 18, 15, 17, 14, 19 };int len = sizeof(arr) / sizeof(arr[0]);//大堆Heap<int> hp1(arr, len);hp1.Print();//小堆Heap<int,LessCompare> hp(arr, len);hp.Print();hp.Push(21);hp.Print();hp.Pop();hp.Print();}

测试结果如下图：

优先级队列的实现就是对上面堆的一层封装，代码如下：

//将堆封装成优先级队列template <class T>class PriorityQueue{public:PriorityQueue(Heap<T>& heap):_heap(heap){}~PriorityQueue(){}void QueuePush(const T& x){_heap.Push();}void QueuePop(){_heap.Pop();}bool QueueEmpty(){return _heap.Empty();}int QueueSize{return _heap.Size();}T& QueueFront(){return _heap.Top();}private:Heap<T> _heap;};