MaxHeap.hpp

/*
 Copyright (c) 2017 waynezxcv <liuweiself@126.com>
 
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 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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#ifndef MaxHeap_hpp
#define MaxHeap_hpp

#include "MaxPriorityQueue.hpp"
#include "IllegalParameterValue.hpp"




/******************** 用堆实现最大优先级队列，大根堆 *******************/


//堆是一个完全二叉树，完全二叉树用数组表示效率最高。大根堆，根节点大于等于他的子节点，如果有的话


namespace LWTL {
    
    template<typename T>
    class MaxHeap : public MaxPriorityQueue<T> {
        
    public:
        
        MaxHeap(int capacity = 10) {
            arrayLength = 10;
            heapSize = 0;
            heap = new T [arrayLength];
        }
        
        ~MaxHeap() {
            delete [] heap;
        }
        
        
        void deactivateArray() {
            heap = NULL;
            arrayLength = heapSize = 0;
        }
        
        bool empty() const override {
            return heapSize == 0;
        }
        
        int size() const override {
            return heapSize;
        }
        
        T& top() const override {
            if (heapSize == 0 ) {
                throw IllegalParameterValue("the heap is empty");
            }
            return heap[1];
        }
        
        
        void push (const T& theElement) override {
            //如果需要的话，扩展数组的空间
            if (heapSize + 1 == arrayLength) {
                T* tmp = new T [arrayLength * 2];
                memset(tmp, 0, sizeof(T) * arrayLength * 2);
                memcpy(tmp, heap, sizeof(T) * heapSize);
                delete [] heap;
                heap = tmp;
            }
            
            int currentNode = ++heapSize;//现在堆的尾部插入一个新结点。heapSize 自增1
            
            //完全二叉树的性质：根节点i = 1.一个标号为i的节点，他的父节点是i/2
            //如果当前结点小于他的根节点,则交换他们
            while (currentNode != 1 && heap[currentNode/2] < heap[currentNode] ) {
                heap[currentNode] = heap[currentNode/2];
                currentNode = currentNode/2;
            }
            heap[currentNode] = theElement;
        }
        
        
        void pop() override {
            
            if (heapSize == 0) {
                throw IllegalParameterValue("the heap is empty");
            }
            
            //先删除根，将最后一个元素放在根部，使堆还是一个完全二叉树
            heap[1].~T();
            
            T theLastElement = heap[heapSize --];//将最后一个元素放在根部，然后heapSize自减1
            
            //从根部向下遍历，将根节点与它的左右孩子比较，将较大者放在根部
            
            int currentNode = 1;
            
            int child = 2;//currentNode的左孩子
            
            while (child <= heapSize) {
                if (child < heapSize && heap[child] < heap[child + 1]) {
                    child ++;
                }
                if (theLastElement < heap[child]) {
                    heap[currentNode] = heap[child];
                    
                    currentNode = child;
                    child = child * 2;
                }
                
            }
            heap[currentNode] = theLastElement;
        }
        
        
        //初始化一个非空大根堆
        void initialize(T* theHeap,int theSize) {
            
            delete [] heap;
            
            heap = theHeap;
            heapSize = theSize;
            
            //堆化,从最后一个具有孩子的结点开始检查。即heapSize/2。检查以这个元素为根的子树是不是大根堆，如果不是则调整。
            //接着减产 heapSize/2 -1.直到根
            for (int root = heapSize/2; root >= 1; root --) {
                
                T rootElement = heap[root];
                
                int child = root * 2;
                
                while (child <= heapSize) {
                    
                    if (child < heapSize && heap[child] < heap[child + 1]) {
                        child ++;
                    }
                    
                    if (rootElement > heap[child]) {
                        break;
                    }
                    
                    heap[child / 2] = heap[child];
                    
                    child *= 2;
                }
                heap[child/2] = rootElement;
            }
        }
        
        
    private:
        
        T* heap;//一个一维数组，保存结点
        int arrayLength;//数组长度
        int heapSize;//堆的大小
        
    };
    
    
}



#endif /* MaxHeap_hpp */