八大排序算法之（四）堆排序

public class HeapSort {

int a[]={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  
 private void 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;  
             }  
         }  
     }  
 }
}