CSE110 Lecture 28

Principles of Programming with Java
Sorting
(202007)

Transcript

1. CSE110 Principles of Programming with Java Lecture 28: Sorting Javier Gonzalez-Sanchez javiergs@asu.edu javiergs.engineering.asu.edu | javiergs.com Office Hours: By appointment
2. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 2 Sorting Sort: arrange values into an order such as Alphabetical, Ascending numeric, or Descending numeric Two algorithms considered here : • Bubble sort • Selection sort
3. Bubble Sort
4. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 4 Bubble sort
5. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 5 Bubble sort
6. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 6 Bubble sort
7. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 7 Bubble sort public static void bubbleSort(int[] array1) { boolean swap; do { swap = false; for (int index=0;index<=array1.length-2;index++) { // compare element at index and at index+1 if (array1[index] > array1[index+1]) { //swap them if they are not in the order int temp = array1[index+1]; array1[index+1] = array1[index]; array1[index] = temp; swap = true } } } while (swap == true); }
8. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 8 Bubble sort public static void bubbleSort(int[] array1) { boolean swap; do { swap = false; for (int index=0;index<=array1.length-2;index++) { // compare element at index and at index+1 if (array1[index] > array1[index+1]) { //swap them if they are not in the order int temp = array1[index+1]; array1[index+1] = array1[index]; array1[index] = temp; swap = true ; } } } while (swap == true); }
9. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 9 More Efficient Bubble sort • Notice that after the 1st pass, the largest element is placed in its final position (right most location). • That indicates that after the 2nd pass, the second largest element will be placed in its final position and so on. • So we can reduce the number of comparisons by 1 for every pass. • If we have n elements in the array, then the 1st pass requires (n-1) comparisons, the second pass requires (n-2) comparisons, and so on.
10. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 10 More Efficient Bubble sort //More efficient version of Bubble Sort public static void bubbleSort2(int[ ] array1) { for(int position=array1.length-2; position>=0; position--) { for (int index=0; index<=position; index++) { //compare the element at index and at index+1 if (array1[index] > array1[index+1]){ //swap them if they are not in the order int temp = array1[index+1]; array1[index+1] = array1[index]; array1[index] = temp; } } } }
11. Selection Sort
12. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 12 Algorithm 1. Selection Sort locates the smallest element in the array and exchanges it with the element in position 0. 2. It locates the next smallest element in the array and exchanges it with the element in position 1. 3. It continues until all elements are in order.
13. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 13 Example 1
14. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 14 Example 1
15. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 15 Example 2
16. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 16 Selection Sort public static void selectionSort (int[] data) { int minIndex; for (int index=0; index<data.length-1; index++) { minIndex = index; for (int scan=index+1;scan<data.length; scan++){ if (data[scan] < data[minIndex]) { minIndex = scan; } } //swap the two elements, data[minIndex] and data[index] int temp = data[minIndex]; data[minIndex] = data[index]; data[index] = temp; } }
17. Sorting Arrays of Objects
18. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 18 Arrays of Objects Student [] array = new Student[4]; array[0] = new Student(”Robert”, 4); array[1] = new Student(”Mary”, 1); array[2] = new Student(”Alice”, 3); array[3] = new Student(”John”, 2); John Mary Alice Robert 4 1 3 2
19. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 19 Arrays of Objects | swap // int temp = data[index_1]; // data[index_1] = data[index_2]; // data[index_2] = temp; How to do this for arrays of objects? John Mary Alice Robert 4 1 3 2
20. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 20 Swap | Arrays of Objects What about Sort (Bubble or Selection)? Search (Linear or Binary)? John Mary Alice Robert 4 1 3 2
21. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 21 What about “Selection Sort” for A of O? // Do changes in the highlighted places public static void selectionSort (int[] data) { int minIndex; for (int index=0; index<data.length-1; index++) { minIndex = index; for (int scan=index+1;scan<data.length; scan++){ if (data[scan] < data[minIndex]) { minIndex = scan; } } //swap the two elements, data[minIndex] and data[index] int temp = data[minIndex]; data[minIndex] = data[index]; data[index] = temp; } }
22. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 22 What about “Binary Search” for A of O? // Do changes in the highlighted places public static int binarySearch (int[] data, int target) { int start = 0, end = data.length-1, middle; int position = -1; //return -1 if not found boolean found = false; while (found == false && start <= end) { middle = (start+end)/2; if (data[middle] == target){ found = true; position = middle; } else if (data[middle] > target) end = middle - 1; else start = middle + 1; } return position; //return -1 if not found }
23. CSE110 - Principles of Programming Javier Gonzalez-Sanchez javiergs@asu.edu Summer 2020 Disclaimer. These slides can only be used as study material for the class CSE110 at ASU. They cannot be distributed or used for another purpose.