空元素冒泡排序的逆序

Question

我正在尝试反转我的冒泡排序，以便所有 null 元素都被推到数组的末尾而不是开始，因为它们现在正在排序。关于如何实现这一点有什么建议吗？

            for (int outerLoop = 0; outerLoop < students.Length-1; outerLoop++)
            {
                for (int innerLoop = 0; innerLoop < students.Length-1; innerLoop++)
                {
                    if (students[outerLoop+1] == null)
                    {
                        var tempObject = students[outerLoop+1];
                        students[outerLoop+1] = students[innerLoop];  
                        students[innerLoop] = tempObject;
                    }
                }
            }

Answer 1

有一种更快、更简单、更稳定的方法，时间复杂度为 O(n)：

  int at = 0;

  for (int i = 0; i < students.Length; ++i)
    if (students[i] != null)
      students[at++] = students[i];

  for (int i = at; i < students.Length; ++i)
    students[i] = null;

但是，如果您坚持使用冒泡排序：我们可以用稍微不同的方式来实现它

  for (bool wrongOrder = true; wrongOrder;) {
    wrongOrder = false;

    for (int i = 1; i < students.Length; i++) {
      if (students[i - 1] == null && students[i] != null) {
        // At least 2 items has wrong order, swap them
        var temp = students[i - 1];
        students[i - 1] = students[i];
        students[i] = temp;

        wrongOrder = true;
      }
    }
  }

Answer 2

更正后的代码：

        for (int outerLoop = 0; outerLoop < students.Length-1; outerLoop++)
        {
            for (int innerLoop = 0; innerLoop < students.Length-1; innerLoop++)
            {
                if (students[innerLoop] == null)
                {
                    var tempObject = students[innerLoop+1];
                    students[innerLoop+1] = students[innerLoop];  
                    students[innerLoop] = tempObject;
                }
            }
        }

这不会对您的数组进行排序，只会删除底部的空值。

事实上你可以取消临时变量：

        for (int outerLoop = 0; outerLoop < students.Length-1; outerLoop++)
        {
            for (int innerLoop = 0; innerLoop < students.Length-1; innerLoop++)
            {
                if (students[innerLoop] == null)
                {
                    students[innerLoop] = students[innerLoop+1];  
                    students[innerLoop+1] = null;
                }
            }
        }

注意： C# 7 introduced tuples 可以在没有临时变量的情况下交换两个变量：

int a = 10;
int b = 2;
(a, b) = (b, a);

这会将 b 分配给 a，将 a 分配给 b。

Answer 3

试试看。您必须测试外部是否为 null 而内部是否为 null :

            for (int outerLoop = 0; outerLoop < students.Length - 1; outerLoop++)
            {
                for (int innerLoop = outerLoop + 1; innerLoop < students.Length; innerLoop++)
                {
                    if ((students[outerLoop] == null) && (students[innerLoop] != null))
                    {
                        var tempObject = students[outerLoop];
                        students[outerLoop] = students[innerLoop];
                        students[innerLoop] = tempObject;
                    }
                }
            }

空元素冒泡排序的逆序

Reverse order of bubble sort of null elements

c#

arrays

sorting

bubble-sort