反向链接列表（通过递归）不起作用

Question

I was trying to write a code to reverse the linked list but getting wrong output. Is there something I am missing.

Here is the function

void reverselinklist( struct node **headreverse)
{
    struct node *p = *headreverse;
    if(p->next == NULL)
    {
        *headreverse = p;
        return;
    }

    reverselinklist(&(p->next));
    p->next->next = p;
    p->next = NULL;

}

After display function

Input 409765
Output 4

Answer 1

*headreverse = p is meaningless. You should set *headreverse = p->next each time to move forward, until the last node is reached.

Anyway, I changed your code to make it work:

void reverselinklist(struct node **headreverse)
{
    struct node *p = *headreverse;
    if(p->next == NULL){
        return;
    }
    *headreverse = p->next;
    reverselinklist(headreverse);
    p->next->next = p;
    p->next = NULL;
}

Answer 2

For single list use two two pointers, to update list as you can not go back.

Here is my code. Hope it will help you to understand concept.

void reverselinklist(struct node** head_ref)
{
    struct node* first;
    struct node* rest;

    first = *head_ref; 
    rest  = first->next;

    if (rest == NULL)
       return;  

    reverselinklist(&rest);
    first->next->next  = first; 

    first->next  = NULL;         

    *head_ref = rest;             
}

If it could me more precise please provide suggestions.

Answer 3

Your headreverse is not being assigned to the new head of the list. Be sure to use 2 arguments for your function, 1) head of the initial list 2) current node(same as your headreverse)

if(p->next == NULL)
{
    *head = p; //instead of headreverse use head
    return;
}