chap10

Java Programming: From Problem Analysis to Program Design, 3e

Chapter 10

Applications of Arrays (Searching and Sorting) and Strings

Java Programming: From Problem Analysis to Program Design, 3e 2

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


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


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,” return location

in array – If item not found, report “failure”


• Suppose that you want to determine whether 27 is in the list • First compare 27 with list[0]; that is, compare 27 with 35

• Because list[0] ≠ 27, you then compare 27 with list[1]

• Because list[1] ≠ 27, you compare 27 with the next element in the list

• Because list[2] = 27, the search stops• This search is successful

Search (continued)


Search (continued)

• Let’s now search for 10 • The search starts at the first element in the

list; that is, at list[0]• Proceeding as before, we see that this time

the search item, which is 10, is compared with every item in the list

• Eventually, no more data is left in the list to compare with the search item; this is an unsuccessful search


Search (continued)


• Using a while (or a for) loop, the definition of the method seqSearch can also be written without the break statement as:

Search (continued)


Sorting a List• Bubble sort

– Suppose list[0...n - 1] is a list of n elements, indexed 0 to n - 1

– We want to rearrange; that is, 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, list[index] and list[index + 1] of list are compared

• If list[index] is greater than list[index + 1], then the elements list[index] and list[index + 1] are swapped, that is, interchanged


Bubble Sort


Bubble Sort (continued)


• It is known that for a list of length n, on average bubble sort makes n(n – 1) / 2 key comparisons and about n(n – 1) / 4 item assignments

• Therefore, if n = 1000, then to sort the list bubble sort makes about 500,000 key comparisons and about 250,000 item assignments



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


Selection Sort (continued)


public static void selectionSort(int[] list, int listLength){ int index; int smallestIndex; int minIndex; int temp;

for (index = 0; index < listLength – 1; index++) { smallestIndex = index; for (minIndex = index + 1; minIndex < listLength; minIndex++) if (list[minIndex] < list[smallestIndex]) smallestIndex = minIndex;

temp = list[smallestIndex]; list[smallestIndex] = list[index]; list[index] = temp; }}



• It is known that for a list of length n, on an average selection sort makes n(n – 1) / 2 key comparisons and 3(n – 1) item assignments

• Therefore, if n = 1000, then to sort the list selection sort makes about 500,000 key comparisons and about 3000 item assignments



Insertion Sort• The insertion sort algorithm sorts the list by moving each element to its proper place


Insertion Sort (continued)


public static void insertionSort(int[] list, int listLength){ int firstOutOfOrder, location; int temp; for (firstOutOfOrder = 1; firstOutOfOrder < listLength; firstOutOfOrder++) if (list[firstOutOfOrder] < list[firstOutOfOrder - 1]) { temp = list[firstOutOfOrder];

location = firstOutOfOrder; do { list[location] = list[location - 1]; location--; } while(location > 0 && list[location - 1] > temp); list[location] = temp; }} //end insertionSort



• It is known that 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, then to sort the list, the insertion sort makes about 250,000 key comparisons and about 250,000 item assignments



Sequential Ordered Searchpublic static int seqOrderedSearch(int[] list, int listLength, int searchItem){ int loc; //Line 1 boolean found = false; //Line 2 for (loc = 0; loc < listLength; loc++) //Line 3 if (list[loc] >= searchItem) //Line 4 { found = true; //Line 5 break; //Line 6 } if (found) //Line 7 if (list[loc] == searchItem) //Line 8 return loc; //Line 9 else //Line 10 return -1; //Line 11 else //Line 12 return -1; //Line 13}


Binary Search

• Can only be performed on a sorted list

• Uses divide and conquer technique to search list


Binary Search Algorithm

• Search item is compared with middle element of list

• If search item < middle element of list, search is restricted to first half of the list

• If search item > middle element of list, search second half of the list

• If search item = middle element, search is complete


Binary Search Algorithm (continued)

• Determine whether 75 is in the list


public static int binarySearch(int[] list, int listLength, int searchItem){ int first = 0; int last = listLength - 1; int mid; boolean found = false;

while (first <= last && !found) { mid = (first + last) / 2; if (list[mid] == searchItem) found = true; else if (list[mid] > searchItem) last = mid - 1; else first = mid + 1; } if (found) return mid; else return –1;} //end binarySearch



Performance of the Binary Search


Performance of the Binary Search (continued)


• Suppose that L is a list of size 1000000 • Since 1000000 1048576 = 220, it follows

that the while loop in binary search will have at most 21 iterations to determine whether an element is in L

• Every iteration of the while loop makes two key (that is, item) comparisons




• To determine whether an element is in L, binary search makes at most 42 item comparisons– On the other hand, on average, a sequential search will

make 500,000 key (item) comparisons to determine whether an element is in L

• In general, if L is a sorted list of size n, to determine whether an element is in L, the binary search makes at most 2log2n + 2 key (item) comparisons


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 vector


Members of the class Vector


Members of the class Vector (continued)


Vectors (continued)

• 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


Vector<String> stringList =

new Vector<String>();

stringList.addElement("Spring");stringList.addElement("Summer");stringList.addElement("Fall");stringList.addElement("Winter");

Vectors (continued)


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_candidate


Programming Example: Election Results (continued)

• Output: election results in a tabular form– Each candidate’s name – Number of votes each candidate received in

each region – Total number of votes each candidate received


Programming Example:Election 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


Programming Example:Election Results (Solution) (continued)

• The solution includes (continued):– Sorting the array candidatesName – Processing the voting data – Calculating the total votes received by each

candidate – Outputting the results in tabular form


Programming Example: Election Results


Programming Example: Election Results (continued)


Additional String Methods


Additional String Methods (continued)


Effects of Some String Methods


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


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


Programming Example: Pig Latin Strings (Sample Runs)


Chapter Summary

• Lists

• Searching lists– Sequential searching– Sequential searching on an order list– Binary Search

• Sorting lists– Bubble Sort – Selection Sort– Insertion Sort


Chapter Summary (continued)

• Programming examples

• The class Vector– Members of the class Vector

• The class String– Additional methods of the class String

chap10

Education