Question

copyRev

void copyRev(node *head1, node *&head2)
{

    stack<int> dat;
    node* curr = head1;
    while(curr!=NULL){
        dat.push(curr->data);
        curr = curr->next;
    }
    while(!dat.empty()){
        append(head2,dat.top());
        dat.pop();
    }

}

append

void append(node* &head, int data){

    if(head==NULL){
        head= new node;
        head->data = data;
        head->next = NULL;
    }
    else{

        node *curr = head;
        while((curr)->next!=NULL){
            (curr) = (curr)->next;
        }
        (curr)->next = new node;
        (curr) = (curr)->next;
        (curr)->data = data;
        (curr)->next = NULL;
    }
}

Well, I’m trying to clone the reverse of a linked list. I know how to reverse a list in place. But this code gives me a Bus error(code dumped).

This is how I call the function in main()

node *head;

    for(int i = 0;i<9;i++){
        append(head,i*i);
    }
    node *revHead;
    printList(head);

    copyRev(head,revHead);
    printList(revHead);

in append() function, I check for NULL head and create a new node if it is NULL. moreover, the append function properly adds the elements to the list. The problem arose only after I called the copyRev procedure.

I have tried in-place reversing and it works. I need to clone the reverse of a linked list. Both Iterative and Recursive solutions are welcome. Also please point out the error in the above code.

This is my own practice problem but not a homework problem

Answer 1

You are not initializing your pointers:

node *head;
node *revHead;

As a result they have indeterminate values (ie they are random).

Using the values in these poitners in any way is undefined behavior. Which can be your error.

Just initialize them:

node*  head     = NULL;
node*  revHead  = NULL;

Recursive reverse of a linked list in place:

void reverse(node*& head)
{
     head = reverse(head, NULL);
}
node* reverse(node* item, node* next)
{
     if (item == NULL)
     {    return next;
     }
     node*  iter = item->next;
     item->next  = next;
     return reverse(iter, item);
}