ECE 242 Spring 2003 Data Structures in Java

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ECE 242 Spring 2003Data Structures in Java

• http//rio.ecs.umass.edu/ece242
• Elementary Sorting Algorithms
• Prof. Lixin Gao

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Todays 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 datai datadata.length-1
• 2. swap it with datai
• 3. if not finishing, repeat 12

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Swap Action (SelectionSorting)
20
8
5
10
7
5
8
20
10
7
5
7
20
10
8
5
7
8
10
20
5
7
8
10
20
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SelectionSort

• SelectionSort(int array)
• for( i0 iltarray.length-1 i )
• // find the minimum value index
• // among arrayi, arrayi1,
  arraylength-1
• int minIndex i
• for( int ji1 jltarray.length-1 j )
• if( arrayj lt arrayminIndex)
• minIndex j

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SelectionSort (continued)

• //swap arrayminIndex with arrayi
• int temp arrayminIndex
• arrayminIndex arrayi
• arrayi temp

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Complete Example

• SelectionSorting.java
• int array new int 5
• // initialize the value
• array0 20 array1 8
• array2 5 array3 10
• array4 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
• temp datai
• shift those elements dataj which greater than
  temp to right by one position
• place temp in its proper position

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Insert Action i1
temp
20
8
5
10
7
8
i 1, first iteration
20
20
5
10
7
8
8
20
5
10
7
---
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Insert Action i2
temp
8
20
5
10
7
5
i 2, second iteration
8
20
20
10
7
5
8
8
20
10
7
5
5
8
20
10
7
---
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Insert Action i3
temp
5
8
20
10
7
10
i 3, third iteration
5
8
20
20
7
10
5
8
10
20
7
---
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Insert Action i4
temp
5
8
10
20
7
7
i 4, forth iteration
5
8
10
20
20
7
5
8
10
10
20
7
5
8
8
10
20
7
5
7
8
10
20
---
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InsertionSort

• InsertionSort(int array)
• int temp, i, j
• for( i1 iltarray.length i )
• temp arrayi
• // assuming array0 arrayi-1 are sorted
• for( ji jgt0 templtarrayj-1 j--)
• arrayj arrayj-1
• // move temp in the correct position
• arrayj temp

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Complete Example

• InsertionSorting.java
• InsertSortingInput.txt (sample input data)
• int array new int 5
• // initialize the value
• inputArray()
• // call InsertionSort method
• InsertionSort(array)