二叉堆的建立

  堆是一棵具有特殊性质的二叉树，堆的基本性质是堆中所有结点的值必须大于或者等于（或小于等于）其孩子结点的值。这也称为堆的性质。堆可以分为最大堆和最小堆，如果要求结点的值必须大于其孩子结点的值，则称其为最大堆，反之，则称其为最小堆。

  堆在形式上表现为一棵完全二叉树。这里，使用数组来建立一个最大堆：假定下标从0开始，所有元素都保存在数组中

public class Heap {
	public int[] array;            
	public int count;              //堆中元素的个数
	public int capacity;           //堆的大小
	public int heap_type;          //最小堆或最大堆
	public Heap(int capacity, int heaptype){
		this.capacity = capacity;
		this.heap_type = heaptype;
		this.count = 0;
		this.array = new int[capacity];
	}
	
	public int Parent(int i){//通过数组位置的规律得到
		if(i<=0 || i>this.count)
			return -1;
		return (i-1)/2;
	}
	
	public void Print(){
		for(int i=0;i<this.count;i++)
			System.out.print(this.array[i]+" ");
	}
	
	//左右孩子
	public int LeftChild(int i){
		int left = 2*i+1;
		if(left>=this.count)
			return -1;
		else
			return left;
	}
	public int RightChild(int i){
		int right = 2*i+2;
		if(right>=this.count)
			return -1;
		return right;
	}
	
	public int GetMaximum(){
		if(this.count==0)
			return -1;
		return this.array[0];
	}
	
	//堆化当前元素
	public void PercolateDown(int i){
		int l,r,max,temp;
		l = LeftChild(i);
		r= RightChild(i);
		if (l==-1 && r ==-1)
			return;
		if(l != -1 && this.array[l]>this.array[i] )
			max = l;
		else
			max = i;
		if(r!=-1&&this.array[r]>this.array[max])
			max = r;
		if(max!=i){
			temp = this.array[i];
			this.array[i] = this.array[max];
			this.array[max] = temp;
			PercolateDown(max);
		}
		
	}
	
	//删除元素
	public int DeleteMax(){
		if(this.count==0)
			return -1;
		int data = this.array[0];
		this.array[0] = this.array[this.count-1];
		this.count--;
		PercolateDown(0);
		return data;
	}
	
	//插入元素
	public int Insert(int data){
		int i;
		if(this.count == this.capacity)
			ResizeHeap();
		this.count++;
		i = this.count-1;
                if(i==0){
            this.array[0] = data;
            return i;
          } 
                while(i>0 && data> this.array[(i-1)/2]){
			this.array[i] = this.array[(i-1)/2];
			i=(i-1)/2;
		}
		this.array[i] = data;
		return i;
	}
	//扩展堆
	public void ResizeHeap(){
		int[] array_old = new int[this.capacity];
		System.arraycopy(this.array, 0, array_old, 0,this.count-1);
		this.array = new int[this.capacity*2];
		if(this.array==null){
			System.out.println("Memory error");
			return;
		}
		for(int i=0;i<this.capacity;i++)
			this.array[i] = array_old[i];
		this.capacity*=2;
		array_old = null;
	}
	
	//清空堆
	public void DestroyHeap(){
		this.count = 0;
		this.array = null;
	}
	
	//数组建堆，取n个输入元素将它们插入空堆中
	public void BuildHeap(Heap h,int[] A,int n){
		if(h==null)
			return;
		while(n > this.capacity)
			h.ResizeHeap();
		for(int i=0;i<n;i++)
			h.array[i] = A[i];
		this.count = n;
		int max = n-1;
		for(int i=(max-1)/2;i>=0;i--)
			h.PercolateDown(i);
	}
	
}