1. CS 18000 Problem Solving and Object Oriented Programming Spring 2019
Section LE2
Week 14: Lecture 28, April
Slides updated: 3:29pm, April 24, 2019
Aditya Mathur
Professor, Department of Computer Science
Purdue University
West Lafayette, IN, USA

2. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Today
Binary trees
Quicksort
A good bye message
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

3. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Binary tree T3 T1 T2
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

4. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Binary tree: Elements
Root
Nodes
Left
link
Right
link
Leaf nodes
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

5. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Binary tree: with data
Data: 12, 8, -2, 11, 17, 99, 3 12 8 17 11 99 -2 3
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

6. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Binary tree: traversal
Inorder: Left, Root, Right 12 8 -2 11 17 99 3
Preorder: Root, Left, Right
Postorder: Left, Right, Root
Level order: Level by level
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

7. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Binary tree: traversal
Inorder: Left, Root, Right 12 8 -2 11 17 99 3
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

8. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Quicksort: The algorithm
Problem: Sort an array:
data=[d0 d1 d2 d3 dN ]
Quicksort(data, 0, N)
Select an element in the array; this is element is known as the pivot.
Partition the array so that the left partition (PLeft) has elements less than pivot and the right partition (PRight) has elements equal to or greater than the pivot.
Apply Quicksort( ) to PLeft and PRight
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

9. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Quicksort: Illustration of partitioning
i=-1
j=0
Pivot
i=-1; j=0 Compare 15 with the pivot (8)
[ ]
15>8; array not changed
j=1; i=-1; compare 3 with 8.
[ ]
3<8; bring 3 to position 0
j=2; i=0; compare 19 with 8
[ ]
12>8; no change
j=3; i=0; compare 2 with 8
[ ]
2<8; move 2 to i+1
j=4; i=1;
[ ]
Exchange pivot with 12
j=4; i=2;
[ ]
Exchange pivot with 12
j=4; i=2;
[ ]
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

10. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Quicksort: Apply quicksort on two subarrays
[ ]
[3 2 ]
[PLeft] Quicksort
[ ]
[PRight] Quicksort
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

11. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Programming
Alan Perlis, the first ACM Turing Award laureate, argued in 1961 that all university students take a course in "computers,'' and that they should all learn programming [...].
The process of preparing programs for a digital computer is especially attractive, not only because it can be economically and scientifically rewarding, but also because it can be an aesthetic experience much like composing poetry or music. —DONALD E. KNUTH, The Art of Computer Programming: Fundamental Algorithms, Vol. 1 (2nd ed., 1973, p. v)
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

12. Computers are beautiful things.
You have learned how to communicate with them.
Enjoy life!
Best wishes for success in whatever you do and where ever you go!
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15

13. ©Aditya Mathur. CS 180. Fall 2019.Week 15
Quiz: 04/24/2019
04/24/2019
©Aditya Mathur. CS 180. Fall 2019.Week 15