数据结构与算法（Java版）_堆

package Heap;

public class MaxHeap {
    private int[] heapArray;
    private int maxSize;
    private int currentSize;
    /*构造函数*/
    public MaxHeap(int mx) throws Exception {
        if(mx < 1) throw new Exception("max size must be >=1");
        maxSize = mx;
        currentSize = 0;
        heapArray = new int[maxSize];
    }
    /*向上渗透,index为下标*/
    private void trickleUp(int index){
        int parent = (index - 1) / 2;
        int bottom = heapArray[index];
        while(index>0 && heapArray[parent]<bottom){
            heapArray[index] = heapArray[parent];
            index = parent;
            parent = (parent - 1) / 2;
        }
        heapArray[index] = bottom;
    }
    /*向下渗透*/
    private void trickleDown(int index){
        int largerChild;
        int top = heapArray[index];
        while(index < currentSize / 2){
            int leftChild = 2 * index + 1;
            int rightChild = 2 * index + 2;
            if(rightChild<currentSize && heapArray[leftChild]<heapArray[rightChild])
                largerChild = rightChild;
            else
                largerChild = leftChild;
            if(top >= heapArray[largerChild])
                break;
            heapArray[index] = heapArray[largerChild];
            index = largerChild;
        }
        heapArray[index] = top;
    }
    public boolean IsEmpty(){
        return currentSize == 0;
    }
    public void Push(int num) throws Exception{
        if(currentSize == maxSize) throw new Exception("MaxHeap id full");
        heapArray[currentSize] = num;
        trickleUp(currentSize);
        currentSize++;
    }
    public int Top(){
        return heapArray[0];
    }
    public void Pop(){
        heapArray[0]=heapArray[--currentSize];
        trickleDown(0);
    }
    public static void main(String[] args) throws Exception {
        System.out.println("测试大顶堆");
        MaxHeap maxHeap = new MaxHeap(100);
        System.out.println(maxHeap.IsEmpty());
        maxHeap.Push(20);
        maxHeap.Push(30);
        maxHeap.Push(40);
        System.out.println(maxHeap.Top());
        maxHeap.Push(90);
        maxHeap.Push(80);
        maxHeap.Push(70);
        System.out.println(maxHeap.Top());
        maxHeap.Pop();
        System.out.println(maxHeap.Top());
        maxHeap.Pop();
        System.out.println(maxHeap.Top());
        maxHeap.Pop();
        System.out.println(maxHeap.Top());
    }
}