最小堆

#include<iostream>
#include<queue> //试着加加const
using namespace std;
const int defaultSize=10;
template<class T>
class MinHeap
{
public:
	MinHeap(int sz = defaultSize);
	MinHeap(T arr[], int n);
	~MinHeap() { delete[] heap; }
	bool push(const T& x);
	bool pop();
	T top();
	bool empty() const { return(currentsize == 0) ? true : false; }
	bool isFull() const { return(currentsize == maxHeapsize) ? true : false; }
private:
	T* heap;
	int currentsize;
	int maxHeapsize;
	void siftDown(int start, int m);
	void siftUp(int start);
};
template<class T>
MinHeap<T>::MinHeap(int sz)
{
	maxHeapsize = (defaultSize < sz) ? sz : defaultSize;
	heap = new T[maxHeapsize];
	if (heap == NULL)
		cout << "分配失败" << endl;
	currentsize = 0;
}
template<class T>
MinHeap<T>::MinHeap(T arr[], int sz)
{
	maxHeapsize = (defaultSize < sz) ? sz : defaultSize;
	heap = new T[maxHeapsize];
	if (heap == NULL)
		cout << "分配失败" << endl;
	currentsize = sz;
	for (int i = 0; i < sz; i++) heap[i] = arr[i];
	int currentPos = (currentsize - 2) / 2;
	while (currentPos >= 0)
	{
		siftDown(currentPos, currentsize - 1);
		currentPos--;
	}
}
template<class T>
void MinHeap<T>::siftDown(int start, int m)
{
	int i = start, j = 2 * i + 1;
	T temp = heap[i];
	while (j <= m)
	{
		if (j<m&&heap[j] > heap[j + 1])j++;
		if (temp <= heap[j]) break;
		else {
			heap[i] = heap[j];
			i = j;
			j = 2 * j + 1;
		}
	}
	heap[i] = temp;
}
template<class T>
void MinHeap<T>::siftUp(int start)
{
	int i = start, j = (i - 1) / 2;
	T temp = heap[i];
	while (j >= 0)
	{
		if (heap[j] <= temp)break;
		else
		{
			heap[i] = heap[j];
			i = j;
			j = (j - 1) / 2;
		}
	}
	heap[j] = temp;
}
template<class T>
bool MinHeap<T>::push(const T& x)
{
	if(currentsize==maxHeapsize)
	{
		cout << "Heap Full" << endl;
		return false;
	}
	heap[currentsize] = x;
	siftUp(currentsize);
	currentsize++;
	return true;
}
template<class T>
bool MinHeap<T>::pop()
{
	if (empty())
	{
		cout << "Heap Empty" << endl;
		return false;
	}
	T x = heap[0];
	heap[0] = heap[currentsize - 1];
	currentsize--;
	siftDown(0, currentsize - 1);
	return true;
}
template<class T>
T MinHeap<T>::top()
{
	return heap[0];
}
int main()
{
	int a[] = { 5,6,2,5,1,7,3,2,1,8 };
	MinHeap<int>s(a, 10);
	while (!s.empty())
	{
		cout << s.top();
		s.pop();
	}
}