C ++交换链表中的相邻节点

Question

I'm having some trouble swapping adjacent nodes in a singly linked list. Here's my swap function:

void swap(std::shared_ptr<ListItem> root, int indexA, int indexB)
{
    if (indexA == 0)
    {
        std::shared_ptr<ListItem> A = root;
        std::shared_ptr<ListItem> B = A->next;

        A->next = B->next;
        B->next = A;
        root = B;
    }
    else if (indexB == 0)
    {
        std::shared_ptr<ListItem> B = root;
        std::shared_ptr<ListItem> A = B->next;

        B->next = A->next;
        A->next = B;
        root = A;
    }
    else
    {
        std::shared_ptr<ListItem> preA = GetNode(root, indexA - 1);
        std::shared_ptr<ListItem> preB = GetNode(root, indexB - 1);
        std::shared_ptr<ListItem> A = preA->next;
        std::shared_ptr<ListItem> B = preB->next;
        std::shared_ptr<ListItem> temp = B->next;

        preA->next = B;
        A->next = temp;
        B->next = A;
    }
}

Now as you can see this code only handles adjacent nodes. That is because I'm only using it in my sort function:

void LinkedList::sort() {
    for (int i = 0; i <= this->getSize(); i++)
    {
        int j = i;
        while (j > 0 && getItem(j) < getItem(j - 1))
        {
            swap(root, (j - 1), j);
            j = j - 1;
        }
    }
}

So every time the swap function is ran, the nodes sent in will be adjacent. My problem is that the way I'm swapping right now I lose nodes along the way, the link between them is broken somewhere but I really don't understand why or where. My guess is that I need to use a temporary node but since, again, I don't understand why or where the link is being broken I also don't know where I would need to use the temporary node.

Also the preB node is never used at the moment, that's a remnant from quite a few failed attempts at a fix. Any tips would be greatly appreciated!

Answer 1

So it turns out my problem was something I had never even considered before. It's this line in the sort function:

for (int i = 0; i <= this->getSize(); i++)

That will always make it go one step too far, and I had added a sort of failsafe to getItem() that made it hard to pin down. Basically in getItem() I said that if the node I'm looking for is a nullptr, return 0. Which is really dumb since it makes it seem as if the problem is in swap() rather than sort().

So I changed that one line to:

for (int i = 0; i < this->getSize(); i++)

And it now works. Really dumb mistake and I apologize for wasting people's time. Also thank you very much @manni66 for helping me figure this out!