How do you copy a linked list into another list?

Question

I'm studying data structures and linked lists, but I'm not getting the concept of how to make a copy of a linked list. Can someone explain this, possibly using pseudocode or C code?

Answer 1

The logic for duplicating a linked list is recursive and based on the following observations:

1. The clone of the empty list is the empty list.
2. The clone of a list with first node x and remaining nodes xs is a copy of x prepended to a clone of xs.

If you encode the linked list in C++, this can be very clean:

struct Node {
    int value;
    Node* next;
};

Node* Clone(Node* list) {
    if (list == NULL) return NULL;

    Node* result = new Node;
    result->value = list->value;
    result->next = Clone(list->next);
    return result;
}

Answer 2

Do you understand how to add a new node to an existing list? And do you understand how to traverse (i.e. iterate over) a list? Copying a list is just performing both of these operations simultaneously (traverse ListA; for each element, copy the element and add it as a new node to ListB).