[数据结构与算法]堆排序--很重要

import org.junit.Test;

import java.util.Arrays;

public class DuiPai {
                 //主方法
    public void LargeHeap(int[] arr){
        if(arr == null || arr.length < 1){
            return;
        }
        for (int i = 0; i < arr.length; i++) {
            largeInsert(arr, i);
        }
        int heapSize = arr.length-1;
        swap(arr, 0, heapSize);
        while(heapSize > 0){
            heapify(arr, 0, heapSize--);
            swap(arr, 0, heapSize);
        }
    }

    public void largeInsert(int[] arr, int i){
                //在存在的大根堆上插入节点
        int tmp;
        while (arr[i] > arr[(i-1)/2]) {
            swap(arr, i, (i-1)/2);
            i = (i-1)/2;
        }
    }

    public void heapify(int[] arr, int index, int size){
                        //调整其中任意一个节点，使整体形成大根堆
        int left = index * 2 + 1;
        while(left < size){
            int largest = left + 1 < size && arr[left + 1] > arr[left] ? left + 1 : left;
            largest = arr[largest] > arr[index] ? largest : index;
            if(largest == index){
                break;
            }
            swap(arr, largest, index);
            index = largest;
            left = index * 2 + 1;
        }
    }

    public void swap(int[] arr, int i, int j){ 
                            //交换两个节点
        int tmp;
        tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }

    @Test
    public void test(){   
                            //测试方法
        int[] arr = {4,5,6,3,7,2,8};
        LargeHeap(arr);
        System.out.println(Arrays.toString(arr));
    }
}