以中间要素为枢轴的QuickSort [英] QuickSort with middle elemenet as pivot

问题描述

我正在尝试搜索有关快速排序如何以中间元素为枢轴的任何解释，但我找不到任何解释.我要寻找的是关于如何逐步对数字进行排序的任何演示，因为它真的很难理解算法.谢谢.

I am trying to search for any explanation on how Quick sort works with middle element as pivot but I couldn't find any. What I am trying to look for is there any demo on how the numbers are sorted step by step because its really hard understanding the algorithms. Thanks.

推荐答案

竖线围绕枢轴:

 61 11 93 74 75 21 12|55|81 19 14 86 19 79 23 44
 44 11 23|19|14 21 12 19                        
 19|11|12 14                                    
 11                                             
    19|12|14                                    
    12                                          
      |19|14                                    
       14                                       
          19                                    
             19|21|23 44                        
            |19|21                              
             19                                 
                21                              
                  |23|44                        
                   23                           
                      44                        
                         81 55 75|86|74 79 93 61
                         81 55|75|61 74 79      
                         74|55|61               
                         55                     
                           |74|61               
                            61                  
                               74               
                                  75|81|79      
                                 |75|79         
                                  75            
                                     79         
                                        81      
                                          |93|86
                                           86   
                                              93
 11 12 14 19 19 21 23 44 55 61 74 75 79 81 86 93

基于Hoare分区方案的这种变化:

Based on this variation of Hoare partition scheme:

void QuickSort(int a[], int lo, int hi) {
    int i, j, p;
    if (lo >= hi)
        return;
    i = lo - 1;
    j = hi + 1;
    p = a[(lo + hi)/2];
    while (1)
    {
        while (a[++i] < p) ;
        while (a[--j] > p) ;
        if (i >= j)
            break;
        swap(a+i, a+j);
    }
    QuickSort(a, lo, j);
    QuickSort(a, j + 1, hi);
}

请注意，枢轴可以在分区步骤结束时出现在左侧或右侧.

Note that the pivot can end up in either the left or right part after partition step.

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