Java演算法之堆排序（HeapSort）

import java.util.Arrays;

publicclass HeapSort {
    inta[]={49,38,65,97,76,13,27,49,78,34,12,64,5,4,62,99,98,54,56,17,18,23,34,15,35,25,53,51};
    public  HeapSort(){
       heapSort(a);
    }

    public  void heapSort(int[] a){
        System.out.println("開始排序");
        int arrayLength=a.length;
        //循環建堆
        for(int i=0;i<arrayLength-1;i++){
            //建堆
            buildMaxHeap(a,arrayLength-1-i);
            //交換堆頂和最後一個元素
            swap(a,0,arrayLength-1-i);
            System.out.println(Arrays.toString(a));
        }
    }

 

    private  void swap(int[] data, int i, int j) {
        // TODO Auto-generated method stub
        int tmp=data[i];
        data[i]=data[j];
        data[j]=tmp;
    }

    //對data數組從0到lastIndex建大頂堆
    privatevoid buildMaxHeap(int[] data, int lastIndex) {
        // TODO Auto-generated method stub
        //從lastIndex處節點（最後一個節點）的父節點開始

        for(int i=(lastIndex-1)/2;i>=0;i--){
            //k保存正在判斷的節點
            int k=i;
            //如果當前k節點的子節點存在
            while(k*2+1<=lastIndex){
                //k節點的左子節點的索引
                int biggerIndex=2*k+1;
                //如果biggerIndex小於lastIndex，即biggerIndex+1代表的k節點的右子節點存在
                if(biggerIndex<lastIndex){
                    //若果右子節點的值較大
                    if(data[biggerIndex]<data[biggerIndex+1]){
                        //biggerIndex總是記錄較大子節點的索引
                        biggerIndex++;
                    }
                }

                //如果k節點的值小於其較大的子節點的值
               if(data[k]<data[biggerIndex]){
                    //交換他們
                    swap(data,k,biggerIndex);
                    //將biggerIndex賦予k，開始while循環的下一次循環，重新保證k節點的值大於其左右子節點的值
                    k=biggerIndex;
                }else{
                    break;
                }
            }
        }
    }
}