详解Java如何实现小顶堆和大顶堆

2024-04-02 19:04:59 865人浏览八月长安

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摘要

大顶堆每个结点的值都大于或等于其左右孩子结点的值小顶堆每个结点的值都小于或等于其左右孩子结点的值对比图实现代码 public class Heapnode{

大顶堆

每个结点的值都大于或等于其左右孩子结点的值

小顶堆

每个结点的值都小于或等于其左右孩子结点的值

对比图

在这里插入图片描述

实现代码


public class Heapnode{
    private int size;//堆大小
    private int[] heap;//保存堆数组

    //初始化堆
    public HeapNode(int n) {
        heap = new int[n];
        size = 0;
    }

    //小顶堆建堆
    public void minInsert(int key){
        int i = this.size;
        if (i==0) heap[0] = key;
        else {
            while (i>0 && heap[i/2]>key){
                heap[i] = heap[i/2];
                i = i/2;
            }
            heap[i] = key;
        }
        this.size++;
    }

    //大顶堆建堆
    public void maxInsert(int key){
        int i = this.size;
        if (i==0) heap[0] = key;
        else {
            while (i>0 && heap[i/2]<key){
                heap[i] = heap[i/2];
                i = i/2;
            }
            heap[i] = key;
        }
        this.size++;
    }

    //小顶堆删除
    public int minDelete(){
        if (this.size==0) return -1;
        int top = heap[0];
        int last = heap[this.size-1];
        heap[0] = last;
        this.size--;
        //堆化
        minHeapify(0);
        return top;
    }

    //大顶堆删除
    public int maxDelete(){
        if (this.size==0) return -1;
        int top = heap[0];
        int last = heap[this.size-1];
        heap[0] = last;
        this.size--;
        //堆化
        maxHeapify(0);
        return top;
    }

    //小顶堆化
    public void minHeapify(int i){
        int L = 2*i,R=2*i+1,min;
        if (L<=size && heap[L] < heap[i]) min = L;
        else min = i;
        if (R <= size && heap[R] < heap[min]) min = R;
        if (min!=i){
            int t = heap[min];
            heap[min] = heap[i];
            heap[i] = t;
            minHeapify(min);
        }
    }

    //大顶堆化
    public void maxHeapify(int i){
        int L = 2*i,R=2*i+1,max;
        if (L<=size && heap[L] > heap[i]) max = L;
        else max = i;
        if (R <= size && heap[R] > heap[max]) max = R;
        if (max!=i){
            int t = heap[max];
            heap[max] = heap[i];
            heap[i] = t;
            maxHeapify(max);
        }
    }

    //输出堆
    public void print(){
        for (int i = 0; i < this.size; i++) {
            System.out.print(heap[i]+" ");
        }
        System.out.println();
    }
}

测试


public class Heap {
    static int[] a = {5,3,6,4,2,1};
    static int n = a.length;
    public static void main(String[] args){
        HeapNode heapNode = new HeapNode(n);
        for (int i = 0; i < n; i++) {
            heapNode.maxInsert(a[i]);
        }
        heapNode.print();
        for (int i = 0; i < n; i++) {
            int min = heapNode.maxDelete();
            System.out.print("堆顶："+min+" 剩下堆元素：");
            heapNode.print();
        }
    }
}