通过交换节点的链表选择排序

Question

作业是通过交换节点而不是值来使用选择排序。当排序算法更改最后一个节点时，它会引发 AttributeError，因为

def min_sort()

中的first.next 似乎没有改变并且为 None。这是代码

class LinkedList:
    class Node:
        def __init__(self, data, next=None):
            self.data, self.next = data, next

    def __init__(self, seq):
        self.front = self.Node(None)
        curr = self.front
        for value in seq:
            curr.next = self.Node(value)
            curr = curr.next

    def swap(self, x, y):
        first = self.front
        while first.next is not None:
            if first.next.data == x.data:
                prevx = first
            if first.next.data == y.data:
                prevy = first
            first = first.next
        x, y = y, x
        prevx.next, prevy.next = x, y
        temp = x.next
        x.next = y.next
        y.next = temp

    def progress(self, first, reverse):
        try:
            solid = first
            while first.next is not None:
                if solid.data > first.next.data and not reverse:
                    self.swap(solid, first.next)
                elif solid.data < first.next.data and reverse:
                    self.swap(solid, first.next)
                first = first.next
        except Exception:
            pass

    def min_sort(self, reverse):
        first = self.front
        while first.next is not None:
            self.progress(first, reverse)
            first = first.next


def min_sort(seq, reverse=False):
    ll = LinkedList(seq)
    ll.min_sort(reverse)
    return ll.get_list()


if __name__ == '__main__':
    seq = (4, 30, 8, 31, 48, 19)
    lst = min_sort(seq)
    print(lst)

Traceback (most recent call last):
  File "/Users/rival/My files/Škola/FMFI UK/2. semester/Programovanie 2/projekt8/riesenie.py", line 66, in <module>
    lst = min_sort(seq)
          ^^^^^^^^^^^^^
  File "/Users/rival/My files/Škola/FMFI UK/2. semester/Programovanie 2/projekt8/riesenie.py", line 60, in min_sort
    ll.min_sort(reverse)
  File "/Users/rival/My files/Škola/FMFI UK/2. semester/Programovanie 2/projekt8/riesenie.py", line 46, in min_sort
    while first.next is not None:
          ^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'next'

我不知道如何更改函数中的引用

min_sort

所以它可以工作

Answer 1

错误是因为代码试图首先访问节点的first.next，而该节点为None。

您可以尝试添加额外的检查来处理这种情况

def min_sort(self, reverse):
    first = self.front
    while first is not None and first.next is not None:
        self.progress(first, reverse)
        first = first.next