6.堆排序（不稳定）

package com.wang.principle;

public class Test2 {
    public static void main(String[] args) {
        int[] arr = {49, 38, 65, 97, 76, 13, 27, 50};
        //int[] c = { 13, 38, 65, 97, 76, 13, 2, 50 };//稳定性判断
        heapSort(arr);
        for (int i : arr) {
            System.out.print(i+" ");
        }
    }
    public static void heapSort(int[] arr) {
        if (arr == null && arr.length < 2) {
            return;
        }
        //先构建大顶堆
        for (int i = 0; i < arr.length; i++) {
            headInsert(arr, i);
        }

        int size = arr.length;
        //每次选大顶堆root节点 size不断减1
        swap(arr, 0, --size);
        while (size > 0) {
            headify(arr, 0, size);
            swap(arr, 0, --size);
        }
    }

    //上升
    public static void headInsert(int[] arr, int cur) {
        while (arr[cur] > arr[(cur - 1) / 2]) {
            swap(arr, cur, (cur - 1) / 2);
            cur = (cur - 1) / 2;
        }
    }

    //下降
    public static void headify(int[] arr, int index, int heapSize) {
        int left = index * 2 + 1;
        while (left < heapSize) {
            int largest = left + 1 < heapSize && arr[left + 1] > arr[left] ? left + 1 : left;//最大值下标
            largest = arr[largest] > arr[index] ? largest : index;
            if (largest == index) {
                break;
            }
            swap(arr, largest, index);
            index = largest;
            left = index * 2 + 1;
        }
    }

    private static void swap(int[] arr, int x, int y) {
        int temp = arr[x];
        arr[x] = arr[y];
        arr[y] = temp;
    }



}