Java排序算法--堆排序

import java.util.Arrays;

/**
 * @Author: PurcellHuang
 * @Date: 2019-08-09 16:44
 */
public class HeapSort {

    /**
     * @Author: PurcellHuang
     * @Date: 2019-08-09 16:49
     * 堆排序
     */
    public static void sort(int []arr){
        int start = (arr.length-1)/2;
        for (int i = start ; i >= 0; i--){
            maxHeap(arr,arr.length,i);
        }
        for (int i = arr.length-1; i > 0;i--){
            int temp = arr[0];
            arr[0] = arr[i];
            arr[i] = temp;
            maxHeap(arr,i,0);
        }

    }

    /**
     * @Author: PurcellHuang
     * @Date: 2019-08-09 16:49
     * 建立大顶堆
     */
    public static void maxHeap(int []arr, int size, int index){
        int leftNode = 2*index+1;
        int rightNode = 2*index+2;
        int max = index;
        if (leftNode < size && arr[leftNode] > arr[max]){
            max = leftNode;
        }
        if (rightNode < size && arr[rightNode] > arr[max]){
            max = rightNode;
        }
        if (max != index){
            int temp = arr[index];
            arr[index] = arr[max];
            arr[max] = temp;
            maxHeap(arr,size,max);
        }
    }

    public static void main(String[] args) {
        int []a = {2,4,5,2,1,88,8,9,21,2,5};
        HeapSort.sort(a);
        System.out.println(Arrays.toString(a));

    }

}