242 ECE Spring 2003
Data Structures in Java
http://rio.ecs.umass.edu/ece242
Elementary Sorting Algorithms
Prof. Lixin Gao
ECE242 Spring 2003 Data Structures in Java, Prof. Gao 1
Today's Topics
Selection Sorting Insertion Sorting
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Sorted Listing
Phone book
sorted by name
Course list in registration Guide
sorted by department sorted by course number
ECE242 roster list
sorted by last name
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Why Sorting?
Without sorting
how can I find your phone number quickly? where is ECE242 course schedule?
In BlockBuster video store, more than 1,000 movies
where is "Matrix"?
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Sorting
Sorting by keys
Easy to find what you want Easy to manage these stuff.
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Sorting Integers
How to sort the integers in this array?
20 8 5 10 7
5
7
8 10 20
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Elementary Sorting Algorithms
Selection Sort Insertion Sort Bubble Sort ......
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Selection Sorting
Main idea:
find the smallest element put it in the first position find the next smallest element put it in the second position ...
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Pseudo-code for Selection Sorting
Step: 1. select the smallest element among data[i]~ data[data.length-1]; 2. swap it with data[i]; 3. if not finishing, repeat 1&2
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Swap Action (SelectionSorting)
20 8 5 5 5 5
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8 20 10 7 7 20 10 8 7 7 8 10 20 8 10 20
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Data Structures in Java, Prof. Gao
SelectionSort
SelectionSort(int[] array){ for( i=0; i<array.length-1; i++ ) { // find the minimum value index // among array[i], array[i+1], ... array[length-1]; int minIndex = i; for( int j=i+1; j<=array.length-1; j++ ) if( array[j] < array[minIndex]) minIndex = j;
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SelectionSort (continued)
//swap array[minIndex] with array[i] int temp = array[minIndex]; array[minIndex] = array[i]; array[i] = } temp; }
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Complete Example
SelectionSorting.java int [] array = new int [5]; // initialize the value array[0] = 20; array[1] = 8; array[2] = 5; array[3] = 10; array[4] = 7; // call SelectionSort method SelectionSort(array);
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Insertion Sorting
Main Idea: Starts by considering the first two elements of the array data, if out of order, swap them Consider the third element, insert it into the proper position among the first three elements. Consider the forth element, insert it into the proper position among the first four elements. ......
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Pseudo-code for Insertion Sorting
Place ith item in proper position:
1. temp = data[i] 2. shift those elements data[j] which greater than temp to right by one position 3. place temp in its proper position
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Insert Action: i=1
temp 8 8 20 8 5 10 7 i = 1, first iteration
20 20 5 10 7
---
8 20 5 10 7
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Insert Action: i=2
temp 5 5 5 --ECE242 Spring 2003
8 20 5 10 7 8 20 20 10 7 8 5 8 20 10 7 8 20 10 7
i = 2, second iteration
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Insert Action: i=3
temp 10 10 --5 5 5 8 20...