How to concatenate two linked lists?

Question

Can anyone help me with this? I'm stuck. I'm trying to concatenate two linked lists. I've created a method that adds a node to the beginning of a list and a second method to concatenate. My first method works, but not my second...
First method:
public static Node insertFirst(Node head, Node node){
          Node newNode = new Node();          // declare and initialize newNode.
          newNode = node;                    // store the new item in the new node.
          newNode.link = head;               // newNode.link points to the head.
          head = newNode;                    // update head to be newNode.
          return head;
     }Here is where I have my problem:
public static Node mergeTwoLists(Node a, Node b){
          Node heada = a;
          Node headb = b;
          if(heada == null)
               return headb;                    //if heada is null then returns list headb.
          else if(headb == null)
               return heada;                    //if headb is null then returns list heada.
          else if(heada == null && headb == null)     //if both lists are null, returns null.
               return null;
          else if(heada.link == null){     //only one element in heada.
               headb = insertFirst(b, a);               // inserts the element in heada into headb.
               return headb;
          }//end else if(heada.link == null).
          else if(headb.link == null){     //only one element in headb.
               heada = insertFirst(a,b);               // inserts the element in headb into heada.
               else {
                    mergeTwoLists(heada.link, headb);
                    return heada;
               }//end else
          return heada;
          }//end mergeTwoLists method.I think in this method I'm only adding the nodes if there is only one node in one of the lists. But if there are more than one element in a list...I'm confused as to how to code the last else statement that contains the recursive call.
Can someone help?
Thanks
aiki985

Answer 1

Can't you just point the tail of A to the head of B?
I don't think I'd do this recursivly at all. Use a
while look to find the last node in A and then link
it to whatever the first element in B is.
while(A.next != null){
A = A.next;
A.next = B;
Java that up a bit and check for nulls and it should
work.o.k. thanks...let me try that. It does seem awkward recursively...
aiki985