Lecture 18: Selection Sort, Quicksort & Merge Sort

1. CompSci 105 SS 2005 Principles of Computer Science Lecture 18: Selection Sort, Quicksort & Merge Sort Lecturer: Santokh Singh

2. Revision: Comparing Growth Rates O(2n) O(n3) O(n2) O(n log n) Faster Code Sequential Search O(n) O(log n) Binary Search O(1) Textbook, p. 378

3. Selection Sort 0 1 2 3 4 5 6 7 C O M P U T E R • How does this algorithm execute the instructions? Show the steps on the next page. • What is it’s Big O notation? Textbook, p. 385-6

4. 0 1 2 3 4 5 6 7 C O M P U T E R Java Code, Textbook, p. 386-7

5. Selection Sort 0 1 2 3 4 5 6 7 C O M P U T E R • What is Bubble Sort? • Is there a more efficient way than using Selection Sort or Bubble Sort? Selection Sort Analysis, Textbook, p. 387-388

6. Algorithm Efficiency Analysing Search Algorithms Limits of Big O Analysis Sorting Selection Sort Merge Sort Algorithm Analysis Quick Sort Algorithm Analysis

7. Merging Sorted Lists (L11.4) 0 1 2 3 C M O P 0 1 2 3 E R T U

8. Merge Sort 0 1 2 3 4 5 6 7 C O M P U T E R Analysis, Textbook, p. 393-398

9. C M E O P R Merge Sort U T Analysis, Textbook, p. 393-398

10. 4 2 2 2 1 1 1 1 1 1 Merge Sort 8 items 4 2 1 1 Analysis, Textbook, p. 393-398

11. Algorithm Efficiency Analysing Search Algorithms Limits of Big O Analysis Sorting Selection Sort Merge Sort Algorithm Analysis Quick Sort Algorithm Analysis

12. Partitioning (as seen in L8) ≥p p <p 0 1 2 3 4 8 3 9 1 7 3 1 7 8 9 Textbook, p. 399

13. Assignment 3 private BinaryTreeNode parseTree(){ /*This is the method that helps you to create a binary tree (BinaryTreeNode) data structure. Return null if the TextField where the users put in the expression is empty. Otherwise store the expression into the binary tree data structure. If there are an invalid input i.e. input other than (x,y,z,1,2,3,+,-,*,/) then an error message should be displayed on the command window. */ return null; }

14. private BinaryTreeNode parseTree(){//recursive method to construct a BinaryTreeNode tree from // textString that was input, e.g. +12. if (textString.length() > 0) { BinaryTreeNode result, left, right; char c = textString.charAt(0); textString = textString.substring(1, textString.length()); //when do we create the children of the tree: if(…) { result = new BinaryTreeNode(“” + c); result.setLeft(…) //recursion… result.setRight(…) //recursion… return result; } //when do we create the leaves of the tree: else if(...) { return new BinaryTreeNode("" + c); } else { // error System.out.println("Parse error: invalid character: " + c); return …; // return null } } else // return null }