Linked Lists

1. Linked Lists • Just another data structure • Dynamic • Grows and shrinks as necessary • A “perfect fit” in memory • Allocate memory when we Add() • A little bit more code • “Slow” access to data

2. Nodes • Each node has a piece/set of data

3. Nodes • Each node has a piece/set of data head 75

4. Nodes • Each node has a piece/set of data • Each node has a reference to the “next” thing in the list head 75 “next” is null – meaning “end of list”

5. Code class Node { int data; Node next;} head 75

6. Code class Node { int data; Node next; // Is this recursive? Not really…} head 75

7. Adding Nodes We can add to the end of the list… head 75

8. Adding Nodes We can add to the end of the list… head 75 21

9. Adding Nodes We can add to the end of the list… head 75 21 99

10. Adding Nodes … we can add to the beginning… head 75

11. Adding Nodes … we can add to the beginning… head 75 temp 13

12. Adding Nodes … we can add to the beginning… head 75 temp 13

13. Adding Nodes … we can add to the beginning… head 75 temp 13

14. Adding Nodes … we can add to the beginning… head 75 13

15. Adding Nodes … we can add to the beginning… head 75 13

16. Adding Nodes … or we can add to the middle head 21 75 99

17. Adding Nodes … or we can add to the middle We want to add 80 head 21 75 99

18. Adding Nodes … or we can add to the middle Special case: Is 80 < 21? If so, add to the beginning! head 21 75 99

19. Adding Nodes … or we can add to the middle Look at this node’s next pointer. If so, add to the beginning! head 21 75 99

20. Adding Nodes … or we can add to the middle Is 80 < 75? Nope… head 21 75 99

21. Adding Nodes … or we can add to the middle So update the current node and look at the next pointer head 21 75 99

22. Adding Nodes … or we can add to the middle Is 80 < 99? Yes! head 21 75 99

23. Adding Nodes … or we can add to the middle Create a temp node for the 80 head 21 75 99 temp 80

24. Adding Nodes … or we can add to the middle Have temp.next point to the 99 head 21 75 99 temp 80

25. Adding Nodes … or we can add to the middle Have the 75 node point to the 80 head 21 75 99 temp 80

26. The Importance of Order What if instead… Have the 75 node’s next pointer point to the 80 head 21 75 99 temp 80

27. The Importance of Order What if instead… Create a temp node for the 80 head 21 75 99 temp 80

28. The Importance of Order What if instead… Have temp’s next pointer point to the 75’s next node? head 21 75 99 temp 80

29. The Importance of Order What if instead… Have temp’s next node point to the 75’s next node? head 21 75 99 temp 80

30. The Importance of Order What if instead… We’ve lost the rest of our list! head 21 75 99 temp 80

31. Why? • We only have access to one variable • Traversing from beginning to end head 21 75 99 temp 80

32. One Other Note head 21 75 80 99 101

33. One Other Note 75 101 80 head 21 99

34. Summary • Dynamic • Grows and shrinks as necessary • A “perfect fit” in memory • Insert • Beginning/end/middle • Order is important • “Slow” access to information because of traversal