Linked Lists

1. Linked Lists

2. Example • We would like to keep a list of inventory records – but only as many as we need • An array is a fixed size • Instead – use a linked list • What are the disadvantages of using a linked list?

3. Linked List Object Object Object next_ptr next_ptr next_ptr Ø • Node – one element of the linked list • Object – data stored in the node – examples? • next_ptr – a pointer to the next node in the list • last node points to NULL

4. Linked List tail Object Object Object head next_ptr next_ptr next_ptr Ø • head keeps track of the head of the list • tail keeps track of the last node in the list • tail not always used

5. Insertion at Head tail new_node Object1 Object2 head next_ptr next_ptr Ø Object3 Insert here next_ptr

6. Insertion at Head tail new_node Object1 Object2 head next_ptr next_ptr Ø Object3 next_ptr • Create new_node • store object in new_node • Point new_node next_ptr to the node head points to

7. Insertion at Head tail new_node Object1 Object2 head next_ptr next_ptr Ø Object3 next_ptr • Create new_node • store object in new_node • Point new_node next_ptr to the node head points to • Point head to new_node

8. Insertion at Head tail Object3 Object1 Object2 head next_ptr next_ptr next_ptr Ø • Does this algorithm work for the list below? new_node tail Ø head Object3 next_ptr

9. Insertion at Head • Create new_node • store object in new_node • Point new_node next_ptr to the node head points to • Point head to new_node • If tail points to NULL • point tail to new_node

10. Insertion at Head new_node tail • Create new_node • store object in new_node • Point new_node next_ptr to the node head points to • Point head to new_node • If tail points to NULL • point tail to new_node Ø head Object3 next_ptr

11. Insertion at Tail tail Object1 Object2 head next_ptr next_ptr Ø Object3 Insert here new_node next_ptr new_node tail Ø head Object3 next_ptr

12. Deletion tail Object3 Object1 Object2 head next_ptr next_ptr next_ptr Ø • Deletion of head • Complexity? • Deletion of tail • Complexity?

13. Insertion/Deletion in Middle tail Object3 Object1 Object2 head next_ptr next_ptr next_ptr Ø • Insert between Object1 and Object2 • Delete Object1

14. Doubly Linked Lists Object1 Object2 Object3 header prev_ptr prev_ptr prev_ptr trailer next_ptr next_ptr next_ptr • Each node keeps a pointer to the next node and to the previous node • Makes some operations (such as insertion at end) more efficient • Costs? • At the beginning and end of the list are sentinel nodes • Simplify insertion/deletion algorithm

15. Doubly Linked Lists Object1 Object2 Object3 header prev_ptr prev_ptr prev_ptr trailer next_ptr next_ptr next_ptr • Insertion and deletion at beginning/end • Insertion and deletion in middle header trailer

16. new_node Doubly Linked Lists Object4 prev_ptr insert here next_ptr Object1 Object2 Object3 header prev_ptr prev_ptr prev_ptr trailer next_ptr next_ptr next_ptr • Insertion

17. new_node Doubly Linked Lists Object4 prev_ptr insert here next_ptr Object1 Object2 Object3 header prev_ptr prev_ptr prev_ptr trailer next_ptr next_ptr next_ptr • Insertion • Set next_ptr of new_node to point to what header points to • Set prev_ptr of node that header points to to point to new_node • Set prev_ptr of new_node to point to header • Set header to point to new_node • Number 1 must come before number 4