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;
                 }
             }
         }
     }
 }