Question

在代码上方运行时，第一个数据透视图返回为3.此透视图在第一个递归方法中传输为2，但在第二个递归中，它不会获取值4.可以使用一个来识别问题。

  class QuickSortRevision{

   int pivot;

   void QuickSort(int[] arr,int low,int high){

        if(low>=high)
        return;

        pivot = quickSortPivot(arr,low,high);//first execution pivot =3

        QuickSort(arr,low,pivot-1);//this is taking 0,2 as parameter;

        QuickSort(arr,pivot+1,high);//but this is not taking 4,8 as parameter;

   }
   int quickSortPivot(int[] arr,int low,int high){

           int temp,index,partition,lindex,hindex;
           lindex=low;
           hindex=high-1;
           partition = arr[high];
           index=high;
           System.out.println("low : "+low+" high "+high);

           while(lindex!=hindex){

               while(arr[lindex]<partition  && (lindex!=hindex) ){
                 lindex++;
               }   

               while(arr[hindex]>partition && (lindex!=hindex) ){
                 hindex--;
               }
                  if( lindex!=hindex)
                  {

                     temp=arr[lindex];
                     arr[lindex]=arr[hindex];
                     arr[hindex]=temp;
                     lindex++;hindex--;
                 }
           }  
           temp=arr[lindex];
           arr[lindex]=partition;
           arr[index]=temp;

      System.out.println("lindex:  "+lindex);
       return lindex; 
   }

void printArray(int[] arr)
{
  for(int element  : arr)
  System.out.print(" "+element);
}

public static void main(String[] args){

   QuickSortRevision qs = new QuickSortRevision();
   int arr[]={17,41,5,22,54,6,29,3,13};
   qs.QuickSort(arr,0,arr.length-1);
   qs.printArray(arr);

}}

Answer 1

第一次调用QuickSort时，类成员pivot被赋值为3.然后对QuickSort的递归调用调用quickSortPivot，其结果被分配给pivot（并且进一步的递归调用也会修改此值）。当对Quicksort的调用返回时，pivot的值已被修改！

你将declre pivot作为方法QuickSort的变量，而不是类QuickSortRevision的实例变量

PS：函数QuickSort应该被称为quickSort

Answer 2

将代码lindex!=hindex替换为lindex<=hindex。因为像lindex > hindex那样。像这样的代码：

   public class QuickSortRevision{

   int pivot;

   static int id = 1;

   void QuickSort(int[] arr,int low,int high){

        if(low>=high)
        return;

        pivot = quickSortPivot(arr,low,high);//first execution pivot =3

        QuickSort(arr,low,pivot-1);//this is taking 0,2 as parameter;

        QuickSort(arr,pivot+1,high);//but this is not taking 4,8 as parameter;

   }


   int quickSortPivot(int[] arr,int low,int high){

           int temp,index,partition,lindex,hindex;
           lindex=low;
           hindex=high - 1;
           partition = arr[high];
           index=high;


           while(lindex <= hindex){


               while(arr[lindex]<partition  && (lindex<=hindex) ){
                 lindex++;
               }   
               while(arr[hindex]>partition && (lindex<=hindex) ){
                     hindex--;
               }
               System.out.println("low : "+low+" high "+high);
              if( lindex<=hindex)
              {

                 temp=arr[lindex];
                 arr[lindex]=arr[hindex];
                 arr[hindex]=temp;
                 lindex++;hindex--;
             }






           }  
           temp=arr[lindex];
           arr[lindex]=partition;
           arr[index]=temp;

           // System.out.println(lindex+" "+arr[lindex]);
           System.out.println("lindex:  "+lindex);
       return lindex; 
   }

void printArray(int[] arr)
{
  for(int element  : arr)
  System.out.print(" "+element);
}




public static void main(String[] args){

   QuickSortRevision qs = new QuickSortRevision();
   int arr[]={17,41,5,22,54,6,29,3,13};
   qs.QuickSort(arr,0,arr.length-1);
   qs.printArray(arr);

}

}

快速排序不起作用

2 个答案: