气泡排序比较计数始终相同 [英] bubble sort comparison count is always the same

问题描述

我无法理解比较的工作原理以及气泡排序（或与此相关的任何排序）中进行的比较。在我的冒泡排序示例代码中：

I am having trouble understanding how comparisons work and how many are made in bubble sort(or any sort for that matter). In my example code for bubble sort:

public class BS
 {
   public static void main (String[] args)
   {
     int[] Array = {5,1,4,2,8};


       System.out.println("Array Before Bubble Sort:");
        for (int element : Array)
         System.out.print(element + " ");

         bubbleSort(Array);

       System.out.println("Array After Bubble Sort:"); 
        for (int element : Array)
         System.out.print(element + " ");
         System.out.print("\n");
}
    public static void bubbleSort(int[] array) 
     { 
      int lastPos; 
      int index;
      int temp; 
      int comp = 0;
      int swap = 0;

     for(lastPos = array.length - 1; lastPos >= 0; lastPos--)
      {
        for(index = 0; index <= lastPos - 1; index++)
        {  
         comp++;
          if(array[index] > array[index + 1])
          { 
           swap++;
           temp = array[index];
           array[index] = array[index + 1];
           array[index + 1] = temp;
         }
        }
       } 
    System.out.println("\nComparisons: " + comp); 
    System.out.println("Swaps: " +swap;
   }

 }

输出是这样的：

Array Before Bubble Sort:
5 1 4 2 8 
Comparisons: 10
Swaps: 4
Array After Bubble Sort:
1 2 4 5 8 

据我所知，交换的数量是正确的，但比较的数量不应该是12吗？的比较结果总是10。对于不同的数组，冒泡排序比较是否有所不同？还是取决于数组的大小？我对此没有任何见解，我感到非常困惑。

As far as I can tell, the number of swaps is correct but shouldn't the number of comparisons be 12? No matter what numbers I put in the array, the number of comparisons is always 10. Aren't bubble sort comparisons different for different arrays? Or it depends on the size of the array? I couldn't find any insight on this and I'm genuinely confused. I'd appreciate some help and I will edit with more information if needed.

推荐答案

如果不检查数组是否已排序，它将始终执行

Without a check to see if your array is sorted, it will always perform a constant number of checks based on the size of the array.

在您的for循环中，如果您可以检查是否使用了整个传递，排除掉任何交换，然后您可以提早退出，这意味着对包含5个元素的已排序数组进行排序仅需要进行4次比较。

In your for loops, if you have a check to see if you did an entire pass without any swaps, then you can exit early which would mean that sorting an already sorted array containing 5 elements would only take 4 comparisons.

在测试算法时，您应始终抛出边缘情况，例如您的算法在

When testing your algorithms you should always throw edge cases at them, for instance what is the outcome of your algorithm on

{}
{1}
{0,0,0,0}
{1,1,3,1,1}
{1,2,3,4,5,6}
{10,9,8,7,6,5,4,3,2,1,}
{1,5,1,5,1,5,1,5,1,5,1}

以及一些真正随机的序列。

As well as a few genuinely random sequences.

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