COP 3503 FALL 2012 Shayan Javed Lecture 18

1. COP 3503 FALL 2012ShayanJavedLecture 18 Programming Fundamentals using Java

2. Data Structures

3. So far... • Looked at Arrays and ArrayLists as our data structures

4. So far... • Looked at Arrays and ArrayLists as our data structures • Very useful, but not always the best options

5. So far... • Looked at Arrays and ArrayLists as our data structures • Very useful, but not always the best options • Going to look at some other data structures

6. Data Structures • Stack • Queue • Linked List • Trees • Graph • Hashtable • etc.

7. Data Structures • Stack • Queue • Linked List • Trees • Graph • Hashtable • etc.

8. Stack • Last-In-First-Out (LIFO) Data Structure

9. Stack • Last-In-First-Out (LIFO) Data Structure • Basically...a stack of data.

10. Stack • Last-In-First-Out (LIFO) Data Structure • Basically...a stack of data. • Used when you want the oldest added data first.

11. Stack • Last-In-First-Out (LIFO) Data Structure • Basically...a stack of data. • Used when you want the oldest added data first. • Abstract data type (can store any kind of data).

12. Stack • Three Operations:

13. Stack • Three Operations: • push(Object): Pushes an object on top of a stack

14. Stack • Three Operations: • push(Object): Pushes an object on top of a stack • pop(): Returns the object at the top of the stack and removes it

15. Stack • Three Operations: • push(Object): Pushes an object on top of a stack • pop(): Returns the object at the top of the stack and removes it • peek(): Returns the object at the top without removing it

16. Stack • Some uses:

17. Stack • Some uses: • “Stack Frame” for method calls.

18. Stack • Some uses: • “Stack Frame” for method calls. • Used for evaluating arithmetic expressions: • (prefix, postfix, infix)

19. Stack • Java provides a Stack class (java.util.Stack)

20. Stack • Java provides a Stack class (java.util.Stack) • Has all the operations

21. Stack • Java provides a Stack class (java.util.Stack) • Has all the operations • But how does it actually store the data? (What’s the “back-end”?)

22. Stack • Java provides a Stack class (java.util.Stack) • Has all the operations • But how does it actually store the data? (What’s the “back-end”?) • Uses the java.util.Vector class (similar to ArrayList)

23. Queue • A First-In-First-Out (FIFO) data structure.

24. Queue • A First-In-First-Out (FIFO) data structure. • Used when you want the oldest added data first.

25. Queue • A First-In-First-Out (FIFO) data structure. • Used when you want the oldest added data first. • Often used for scheduling (handle first in line)

26. Queue • Three Operations: • enqueue(Object): Adds an object to the queue • dequeue(): Returns the object at the front of the queue and removes it • peek(): Returns the object at the front without removing it

27. Queue • Java provides a Queue interface (java.util.Queue)

28. Queue • Java provides a Queue interface (java.util.Queue) • Has all the operations • enqueue = add • dequeue = poll

29. Queue • Java provides a Queue interface (java.util.Queue) • Has all the operations • enqueue = add • dequeue = poll • Interface implemented in classes like LinkedList

30. Queue • Java provides a Queue interface (java.util.Queue) • Has all the operations • enqueue = add • dequeue = poll • Interface implemented in classes like LinkedList Queue<Integer> queue = newLinkedList<Integer>();

31. Arrays and ArrayLists • Work well in a lot of cases.

32. Arrays and ArrayLists • Work well in a lot of cases. • Can use as “back-end” data structures

33. Arrays and ArrayLists • Work well in a lot of cases. • Can use as “back-end” data structures • But where do they fall short?

34. Arrays and ArrayLists • Work well in a lot of cases. • Can use as “back-end” data structures • But where do they fall short? • Data retrieval – excellentO(1)

35. Arrays and ArrayLists • Work well in a lot of cases. • Can use as “back-end” data structures • But where do they fall short? • Data retrieval – excellentO(1) • Adding data

36. Arrays and ArrayLists • Work well in a lot of cases. • Can use as “back-end” data structures • But where do they fall short? • Data retrieval – excellentO(1) • Adding data – inefficientO(n) in some cases

37. Arrays and ArrayLists • Work well in a lot of cases. • Can use as “back-end” data structures • But where do they fall short? • Data retrieval – excellentO(1) • Adding data – inefficientO(n) in some cases

38. Arrays and ArrayLists • Work well in a lot of cases. • Can use as “back-end” data structures • But where do they fall short? • Data retrieval – excellentO(1) • Adding data – inefficientO(n) in some cases • Fixed size – have to shift/copy to new array

39. Arrays and ArrayLists • What if your application requires a lot of adds but not retrievals?

40. Arrays and ArrayLists • What if your application requires a lot of adds but not retrievals? • Use Linked Lists

41. Linked List • A list – a collection of linked nodes.

42. Linked List • A list – a collection of linked nodes. • Dynamic data structure – size is not fixed, and memory is not contiguous (unlike an array)

43. Linked List • A list – a collection of linked nodes. • Dynamic data structure – size is not fixed, and memory is not contiguous (unlike an array) • Insertion to the list is very fast – O(1) in most cases

44. Linked List • A list – a collection of linked nodes. • Dynamic data structure – size is not fixed, and memory is not contiguous (unlike an array) • Insertion to the list is very fast – O(1) in most cases • Indexing is slow. Random access also not possible

45. Linked List • Many variations: • Singly-Linked List(can only traverse forward) • Doubly-Linked List (can traverse in reverse too) • Circular Linked Lists • Multi-Linked Lists • etc.

46. Node • Basic structure – collection of linked nodes make a linked list.

47. Node • Basic structure – collection of linked nodes make a linked list. • Stores some data and a link to the next Node.

48. Node • Basic structure – collection of linked nodes make a linked list. • Stores some data and a link to the next Node. int null

49. Node • Basic structure – collection of linked nodes make a linked list. • Stores some data and a link to the next Node. int int null

50. Singly-Linked List (SLL) • Nodes connected to each other