Help: reverse a linked list

[Hamster]

Hi,

Need help with my code on reversing a singly linked list, here's my
code:

void reverseList ( List& listObj)
{

ListNode*pHeadnew=listObj.lastPtr, *pTailnew=listObj.firstPtr;

ListNode* p1=listObj.firstPtr, *p2=listObj.firstPtr->nextPtr, *p3=p2-

nextPtr;

while (p3!=0)
{
p2->nextPtr=p1;
p1=p2;
p2=p3;
p3=p3->nextPtr;
}

listObj.firstPtr=pHeadnew;
listObj.lastPtr=pTailnew;
listObj.lastPtr->nextPtr=0;
}

My test code created a 5-node list, after calling this function
(declared as friend in class List), the resulting list has only 1 node
left.

May anyone help spot what is wrong?

Thanks.

 

[Obnoxious User]

Fixed it myself, thanks.

Is there any way to delete your own post?

If you're religious, you could beg to your deity of choice.
The answer is no, your post is forever archived.

 

[Hamster]

Fixed it myself, thanks.

Is there any way to delete your own post?

 

[Hamster]

Alf,

I missed some if/else structure when copying/pasting which left that
piece of code logically incomplete and confusing.

Thank you for your time.

OU,

Thanks to confirm...would be nice if there were such a feature, imo.

 

[Chris M. Thomasson]

Hi,

Need help with my code on reversing a singly linked list, here's my
code:

________________________________________________________
node* reverse(node* list) {
node* head = NULL;
while (list) {
node* const next = list->next;
list->next = head;
head = list;
list = next;
}
return head;
}
________________________________________________________

 

[Pascal J. Bourguignon]

node* reverse1(node* list,node* result){
if(list){
node* next=list->next;
return(reverse1(next,(list->next=result,list)));
}else{
return(result);
}
}
node* nreverse(node* list){
return(reverse1(list,0));
}
// Notice that g++ -O3 implements TCO, so there's no recursive call here.


With better definitions it could be written as:

node* reverse1(node* list,node* result){
return(list?reverse1(rest(list),cons(first(list),result)):result); }
node* reverse(node* list){
return(reverse1(list,0)); }
// Still no recursive call, thanks to TCO.


that is:

struct node {
char* first;
node* rest;
node(char* aFirst,node* aRest):first(aFirst),rest(aRest){};
};

char* first(node* node){return(node->first);}
ndoe* rest(node* node){return(node->rest);}
node* cons(char* first,node* rest){return(new node(first,rest));}

________________________________________________________
node* reverse(node* list) {
node* head = NULL;
while (list) {
node* const next = list->next;
list->next = head;
head = list;
list = next;
}
return head;
}
________________________________________________________

This works ok, so what else do you want?

 

[Jorgen Grahn]

Fixed it myself, thanks.

Is there any way to delete your own post?

There used to be, but people started disabling it fifteen years ago
due to abuse. It's called /cancelling/ a posting.

In either case, it's more polite to show us your error and the
solution.

/Jorgen