Copy a linked list

Question

typedef struct Node
{
  int data;
  Node *next;
  Node *other;
};

Node *pHead;

pHead is a singly linked list. The next f

Answer 1

Came across this. Hope it helps!

Citing one solution from this link, below.

1) Create the copy of 1 and insert it between 1 & 2, create the copy of 2 and insert it between 2 & 3.. Continue in this fashion, add the copy of N to Nth node

2) Now copy the arbitrary link in this fashion

 if original->arbitrary is not NULL
   original->next->arbitrary = original->arbitrary->next;  /*TRAVERSE TWO NODES*/
 else
   original->next->arbitrary=NULL;

This works because original->next is nothing but copy of original and Original->arbitrary->next is nothing but copy of arbitrary.

3) Now restore the original and copy linked lists in this fashion in a single loop.

 original->next = original->next->next;
 copy->next = copy->next->next;

4) Make sure that last element of original->next is NULL.

Sample code, Time Complexity O(N), Space Complexity O(1)

pNode copy_list(pNode head) {
  // pre-condition: node->other either points into the list or NULL
  if (!head) return NULL;

  pNode node = head, copied = NULL, cnode = NULL;
  for ( ; node; node = node->next->next) {
    // make copy
    cnode = newnode(node->next, node->data);
    cnode->other = node->other;
    if (node == head)
      copied = cnode;

    // insert the copy between originals    
    node->next = cnode;    
    // node -> cnode -> (orig)node->next
  }

  for (node = head; node && node->next; 
       node = node->next->next /* only original nodes */) 
    if (node->other)
      node->next->other = node->other->next;
    else
      node->next->other = NULL;    

  // restore lists
  node = head; cnode = copied;
  for ( ; cnode && cnode->next; node = node->next, cnode = cnode->next) { 
    node->next = node->next->next;
    cnode->next = cnode->next->next;
  }
  node->next = NULL;
  return copied;
}

Complete program is at http://gist.github.com/349630