Chapter 14: Searching and Sorting

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Chapter 14 Searching and Sorting

• Java Programming
• From Problem Analysis to Program Design,
• Fourth Edition

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Chapter Objectives

• Learn how to implement the sequential search
  algorithm.
• Explore how to sort an array using bubble sort,
  selection sort, and insertion sort algorithms.
• Learn how to implement the binary search
  algorithm.
• Become aware of the class Vector.
• Learn more about manipulating strings using the
  class String.

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List Processing

• List A set of values of the same type.
• Basic operations performed on a list
• Search list for given item.
• Sort list.
• Insert item in list.
• Delete item from list.

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Search

• Necessary components to search a list
• Array containing the list.
• Length of the list.
• Item for which you are searching.
• After search completed
• If item found, report success and return
  location in array.
• If item not found, report failure.

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Search

• public static int seqSearch(int list,
• int listLength, int searchItem)
• int loc
• boolean found false
• for (loc 0 loc lt listLength loc)
• if (listloc searchItem)
• found true
• break
• if (found)
• return loc
• else
• return -1

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Sorting a List

• Bubble sort
• Suppose list0...n - 1 is a list of n elements,
  indexed 0 to n - 1. We want to rearrange (sort)
  the elements of list in increasing order. The
  bubble sort algorithm works as follows
• In a series of n - 1 iterations, the successive
  elements, listindex and listindex 1, of
  list are compared. If listindex is greater than
  listindex 1, then the elements listindex
  and listindex 1 are swapped (interchanged).

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Bubble Sort
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Bubble Sort
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Bubble Sort
public static void bubbleSort(int list,
int listLength) int
temp int counter, index for (counter
0 counter lt listLength - 1
counter) for (index 0
index lt listLength - 1 counter
index) if (listindex gt
listindex 1)
temp listindex listindex
listindex 1 listindex 1
temp
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Bubble Sort

• For a list of length n, an average bubble sort
  makes n(n 1) / 2 key comparisons and about n(n
  1) / 4 item assignments.
• Therefore, if n 1000, bubble sort makes about
  500,000 key comparisons and about 250,000 item
  assignments to sort the list.

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Selection Sort

• List is sorted by selecting list element and
  moving it to its proper position.
• Algorithm finds position of smallest element and
  moves it to top of unsorted portion of list.
• Repeats process above until entire list is sorted.

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Selection Sort
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Selection Sort
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Selection Sort
public static void selectionSort(int list,
int listLength)
int index int smallestIndex int
minIndex int temp for (index 0 index
lt listLength 1 index)
smallestIndex index for (minIndex
index 1 minIndex lt listLength
minIndex) if (listminIndex lt
listsmallestIndex)
smallestIndex minIndex temp
listsmallestIndex listsmallestIndex
listindex listindex temp
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Selection Sort

• For a list of length n, an average selection sort
  makes n(n 1) / 2 key comparisons and 3(n 1)
  item assignments.
• Therefore, if n 1000, selection sort makes
  about 500,000 key comparisons and about 3000 item
  assignments to sort the list.

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Insertion Sort
The insertion sort algorithm sorts the list by
moving each element to its proper place.
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Insertion Sort
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Insertion Sort
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Insertion Sort
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Insertion Sort
public static void insertionSort(int list,
int noOfElements)
int firstOutOfOrder, location int temp
for (firstOutOfOrder 1
firstOutOfOrder lt noOfElements
firstOutOfOrder) if (listfirstOutOfOrder
lt listfirstOutOfOrder - 1) temp
listfirstOutOfOrder location
firstOutOfOrder do
listlocation listlocation - 1
location-- while(location gt 0
listlocation - 1 gt temp)
listlocation temp //end insertionSort
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Insertion Sort

• For a list of length n, on average, the insertion
  sort makes (n2 3n 4) / 4 key comparisons
  and about n(n 1) / 4 item assignments.
• Therefore, if n 1000, the insertion sort makes
  about 250,000 key comparisons and about 250,000
  item assignments to sort the list.

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Sequential Ordered Search
public static int seqOrderedSearch(int list,
int listLength, int searchItem)
int loc
//Line 1 boolean found false
//Line 2 for (loc 0 loc lt
listLength loc) //Line 3 if
(listloc gt searchItem) //Line 4
found true
//Line 5 break
//Line 6 if (found)
//Line 7
if (listloc searchItem) //Line 8
return loc
//Line 9 else
//Line 10 return -1
//Line 11 else
//Line 12 return
-1 //Line 13
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Binary Search

• Can only be performed on a sorted list.
• Uses divide and conquer technique to search list.
• If L is a sorted list of size n, to determine
  whether an element is in L, the binary search
  makes at most 2 log2n 2 key comparisons.
• (Faster than a sequential search.)

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Binary Search Algorithm

• Search item is compared with middle element of
  list.
• If search item lt middle element of list, search
  is restricted to first half of the list.
• If search item gt middle element of list, search
  is restricted to second half of the list.
• If search item middle element, search is
  complete.

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Binary Search Algorithm
Determine whether 75 is in the list.
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Binary Search Algorithm
public static int binarySearch(int list, int
listLength, int
searchItem) int first 0 int last
listLength - 1 int mid boolean found
false while (first lt last !found)
mid (first last) / 2 if
(listmid searchItem) found
true else if (listmid gt
searchItem) last mid - 1
else first mid 1
if (found) return mid else
return 1 //end binarySearch
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Vectors

• The class Vector can be used to implement a list.
• Unlike an array, the size of a Vector object can
  grow/shrink during program execution.
• You do not need to worry about the number of data
  elements in a vector.

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Members of the class Vector
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Members of the class Vector
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Members of the class Vector
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Members of the class Vector
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Vectors

• Every element of a Vector object is a reference
  variable of the type Object.
• To add an element into a Vector object
• Create appropriate object.
• Store data into object.
• Store address of object holding data into Vector
  object element.

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Vectors
VectorltStringgt stringList new
VectorltStringgt() stringList.addElement("Spring")
stringList.addElement("Summer") stringList.addE
lement("Fall") stringList.addElement("Winter")
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Programming Example Election Results

• Input Two files
• File 1 Candidates names
• File 2 Voting data
• Voting data format
• candidate_name region number_of_votes_for_this_ca
  ndidate

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Programming Example Election Results

• Output Election results in a tabular form.
• Each candidates name.
• Number of votes each candidate received in each
  region.
• Total number of votes each candidate received.

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Programming ExampleElection Results (Solution)

• The solution includes
• Reading the candidates names into the array
  candidateName.
• A two-dimensional array consisting of the votes
  by region.
• An array consisting of the total votes parallel
  to the candidateName array.

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Programming ExampleElection Results (Solution)

• Sorting the array candidatesName.
• Processing the voting data.
• Calculating the total votes received by each
  candidate.
• Outputting the results in tabular form.

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Programming Example Election Results
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Programming Example Election Results
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Additional String Methods
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Additional String Methods
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Additional String Methods
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Additional String Methods
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Effects of Some String Methods
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Programming Example Pig Latin Strings

• If string begins with a vowel, -way is appended
  to it.
• If first character is not a vowel
• Add - to end.
• Rotate characters until the first character is a
  vowel.
• Append ay.
• Input String
• Output String in pig Latin

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Programming Example Pig Latin Strings (Solution)

• Methods isVowel, rotate, pigLatinString
• Use methods to
• Get the string (str).
• Find the pig Latin form of str by using the
  method pigLatinString.
• Output the pig Latin form of str.

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Programming Example Pig Latin Strings (Sample
Runs)
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Chapter Summary

• Lists
• Searching lists
• Sequential searching
• Sequential searching on an order list
• Binary search
• Sorting lists
• Bubble sort
• Selection sort
• Insertion sort

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Chapter Summary

• Programming examples
• The class Vector
• Members of the class Vector
• The class String
• Additional methods of the class String