Question

我的Quicksort算法遇到了一些麻烦。它在没有重复值的数组上运行良好。但是，一旦我有一个2+重复的数组，它就会陷入无限循环。例如，如果我的数组是：

int[] array = {44, 53, 36, 186, 22, 162, 22};



public void quick_sort(int[] data, int low, int high)
   {  // 1 or 0 items are sorted by default
      if(high - low < 1)
         return;

      int left = low;
      int right = high;
      int pivot = data[low + (high - low) / 2];  

      while(left < right)
      {  // Increment left pointer until left >= pivot
         while(data[left] < pivot)
            left++;

         // Increment right pointer until right <= pivot
         while(data[right] > pivot)
            right--;

         // If left <= right; swap values
         if(left <= right)
         {  int temp = data[right];
            data[right] = data[left];
            data[left] = temp;
         }
      }

      // quick_sort 'lesser values'
      quick_sort(data, low, left - 1);
      // quick_sort 'greater values'
      quick_sort(data, left + 1, high);
   }

提前感谢您的帮助。

解决：

   public void quick_sort(int[] data, int low, int high)
   {  // 1 or 0 items are sorted by default
      if(high - low < 1)
         return;

      int left = low;
      int right = high;
      int pivot = data[low + (high - low) / 2];  

      while(left <= right)
      {  // Increment left pointer until left >= pivot
         while(data[left] < pivot)
            left++;

         // Increment right pointer until right <= pivot
         while(data[right] > pivot)
            right--;

         // If left < right; swap values
         if(left <= right)
         {  int temp = data[left];
            data[left] = data[right];
            data[right] = temp;
            left++;
            right--;
         }

      }
      // quick_sort 'lesser values'
      quick_sort(data, low, right);

      // quick_sort 'greater values'
      quick_sort(data, left, high);
   }

Answer 1

好吧，有了重复项，您可以获得(left < right)但data[left] == pivot == data[right]。

在这种情况下，你的循环不会向左或向右递增，它只是一次又一次地交换元素......（即使在left==right时也很有趣“交换”）

Answer 2

考虑data[left] == data[right] == pivot时会发生什么。

Quicksort w /重复错误

2 个答案: