Why is temporary Node necessary in Reversing a linked list in cpp?-CodePudding

Here is the working code:

Node* Reverse(Node *head)
{
    Node *prev = NULL;
    Node *next;
    Node *current = head;
    while (current != NULL)
    {
        next = current -> next;
        current -> next = prev;
        prev = current;
        current = next;
    }
    head = prev;

    return head;
}

And this doesn't work when I remove the temporary variable current.

Node* Reverse(Node *head)
{
    Node *prev = NULL;
    // Node *current = head;
    Node *next;
    while (head != NULL)
    {
        next = head -> next;
        head -> next = prev;
        prev = head;
        head = next;
    }
    return head;
}

I understand that we need next since we have to keep track of it before losing access to it. But I cannot think of why the temporary variable current is necessary? Any help would be appreciated.

CodePudding user response：

You don't need the current variable. (despite it's name head would be confusing)

The code is different because you don't assign prev to head in the second snippet.

Node* Reverse(Node *head)
{
    Node *prev = NULL;
    // Node *current = head;
    Node *next;
    while (head != NULL)
    {
        next = head -> next;
        head -> next = prev;
        prev = head;
        head = next;
    }
    
    // or head=prev; return head;
    return prev; // <--- 
}