算法-java代码实现堆排序

import java.util.*;

public class HeapSort {

    public int[] heapSort(int[] A, int n) {

        int lastIndex = n - 1;

        buildMaxHeap(A, lastIndex);//建立最大堆

        while(lastIndex > 0){

            swap(A, 0, lastIndex);

            if(--lastIndex == 0)//只剩一个元素，就不用调整堆了，排序结束

                break;

            adjustHeap(A,0,lastIndex);    

        }

        return A;

    }

    public void buildMaxHeap(int[] arr, int lastIndex) {

        // 从最后一个元素的父节点开始进行调整，一直调整到根节点结束

        int j = (lastIndex - 1) / 2;

        while (j >= 0) {

            int rootIndex = j;

            adjustHeap(arr, rootIndex, lastIndex);

            j--;

        }

    }

    public void adjustHeap(int[] arr, int rootIndex, int lastIndex) {//从根节点开始往下调整

        int biggerIndex = rootIndex;

        int leftChildIndex = rootIndex * 2 + 1; 

        int rightChildIndex = rootIndex * 2 + 2;

        if(rightChildIndex <= lastIndex){//如果右孩子存在，则左孩子一定存在

            if(arr[rightChildIndex] > arr[rootIndex] || arr[leftChildIndex] > arr[rootIndex]){

                //将子节点更大的元素下标赋值给biggerIndex

                biggerIndex = arr[rightChildIndex] > arr[leftChildIndex]?rightChildIndex:leftChildIndex;

            }

        }

        else if(leftChildIndex <= lastIndex){//保证左孩子存在，且不能越界

            if(arr[leftChildIndex] > arr[rootIndex]){

                biggerIndex = leftChildIndex;

            }

        }

        if(biggerIndex != rootIndex){

            swap(arr, biggerIndex, rootIndex);

            adjustHeap(arr, biggerIndex, lastIndex);

        }

    }

    public void swap(int[] arr, int biggerIndex, int rootIndex) {

        int temp = arr[rootIndex];

        arr[rootIndex] = arr[biggerIndex];

        arr[biggerIndex] = temp;

    }

}