Merging two sorted linked lists

Question

This is one of the programming questions asked during written test from Microsoft. I am giving the question and the answer that I came up with. Thing is my answer although l

Answer 1

The most glaring bug is in your loop, you keep overwriting mergedList->next, losing the previously added node. That is, your returned list will never contain more than two nodes, regardless of input ...

It's been a while since I did C, but I would do it as follows:

Node* merge(Node* list1, Node* list2) {
    Node* merged = null;
    Node** tail = &merged;

    while (list1 && list2) {
        if (list1->data < list2->data) {
            *tail = list1;
            list1 = list1->next;
        } else {
            *tail = list2;
            list2 = list2->next;
        }
        tail = &((*tail)->next);
    }
    *tail = list1 ? list1 : list2;
    return merged;
}

Answer 2

You can use recursion:

Node* MergeLists(Node *headA, Node* headB)
{

if(headA==NULL){
    return headB;
}else if(headB ==NULL){
    return headA;
}
Node* head = NULL;
if(headA->data <= headB->data){
    head= headA;
    head->next = MergeLists(headA->next,headB);
}else{
    head= headB;
    head->next = MergeLists(headA,headB->next);
}
 return head;
}