Question

I am implementing a function to recursively reverse a linked-list, but getting seg-fault.

typedef struct _node {
   int data;
   struct _node *next;
} Node, *NodeP;

NodeP recursiveReverseList(NodeP first){
   if(first == NULL) return NULL;
   if(first->next == NULL) return first;

   NodeP rest = recursiveReverseList(first->next);
   rest->next = first;
   first->next = NULL;

   return first;
}

Can you please help?

P.S. The iterative version is working fine though. Its not homework. Just practicing C.

Thank you all 🙂

Answer 1

@Unicornaddict has already posted a correct algorithm.

But, if you are still getting segmentation fault, I suspect you are making some mistake in calling the function from main.

Correct:

head->next = recursiveReverseList(head->next);

Explanation:

• Pass head->next to the recursive function. If you pass head, it will do something like

Before call:
head —> A —> B —> C
After call:
head <— A <— B <— C

which will make head point to NULL and A point to head

• After passing head->next as argument, state of the list is:

head —> A <— B <— C

So, you need to make head point to rest (C in this case).