Chapter Objectives. List Processing. Chapter 10: Applications of Arrays and Strings. Java Programming: Program Design Including Data Structures

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1 Chapter 10: Applications of Arrays and Strings Java Programming: Program Design Including Data Structures 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 Java Programming: Program Design Including Data Structures 2 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 Java Programming: Program Design Including Data Structures 3 1

2 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 Java Programming: Program Design Including Data Structures 4 Search (continued) public static int seqsearch(int[] list, int listlength, int searchitem) int loc; boolean found = false; for (loc = 0; loc < listlength; loc++) if (list[loc] == searchitem) found = true; break; if (found) return loc; else return -1; Java Programming: Program Design Including Data Structures 5 Sorting a List Bubble sort Suppose list[0...n - 1] is a list of n elements We want to rearrange (sort) the elements of list 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 (interchanged) Java Programming: Program Design Including Data Structures 6 2

3 Bubble Sort Java Programming: Program Design Including Data Structures 7 Bubble Sort (continued) Java Programming: Program Design Including Data Structures 8 Bubble Sort (continued) public static void bubblesort(int list[], int listlength) int temp; int counter, index; for (counter = 0; counter < listlength - 1; counter++) for (index = 0; index < listlength - 1 counter; index++) if (list[index] > list[index + 1]) temp = list[index]; list[index] = list[index + 1]; list[index + 1] = temp; Java Programming: Program Design Including Data Structures 9 3

4 Bubble Sort (continued) 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 Java Programming: Program Design Including Data Structures 10 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 Java Programming: Program Design Including Data Structures 11 Selection Sort (continued) Java Programming: Program Design Including Data Structures 12 4

5 Selection Sort (continued) Java Programming: Program Design Including Data Structures 13 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; Selection Sort (continued) temp = list[smallestindex]; list[smallestindex] = list[index]; list[index] = temp; Java Programming: Program Design Including Data Structures 14 Selection Sort (continued) 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 Java Programming: Program Design Including Data Structures 15 5

6 Insertion Sort The insertion sort algorithm sorts the list by moving each element to its proper place Java Programming: Program Design Including Data Structures 16 Insertion Sort (continued) Java Programming: Program Design Including Data Structures 17 Insertion Sort (continued) Java Programming: Program Design Including Data Structures 18 6

7 Insertion Sort (continued) Java Programming: Program Design Including Data Structures 19 Insertion Sort (continued) public static void insertionsort(int[] list, int noofelements) int firstoutoforder, location; int temp; for (firstoutoforder = 1; firstoutoforder < noofelements; 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 Java Programming: Program Design Including Data Structures 20 Insertion Sort (continued) For a list of length n, on average, the insertion sort makes (n 2 + 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 Java Programming: Program Design Including Data Structures 21 7

8 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 < 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 Java Programming: Program Design Including Data Structures 22 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 * log 2 n + 2 key comparisons Faster than a sequential search Java Programming: Program Design Including Data Structures 23 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 is restricted to second half of the list If search item = middle element, search is complete Java Programming: Program Design Including Data Structures 24 8

9 Binary Search Algorithm Determine whether 75 is in the list. Java Programming: Program Design Including Data Structures 25 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 <= 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 Java Programming: Program Design Including Data Structures 26 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 Java Programming: Program Design Including Data Structures 27 9

10 Members of the class Vector Java Programming: Program Design Including Data Structures 28 Members of the class Vector (continued) Java Programming: Program Design Including Data Structures 29 Members of the class Vector (continued) Java Programming: Program Design Including Data Structures 30 10

11 Members of the class Vector (continued) Java Programming: Program Design Including Data Structures 31 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 Java Programming: Program Design Including Data Structures 32 Vectors (continued) Vector<String> stringlist = new Vector<String>(); stringlist.addelement("spring"); stringlist.addelement("summer"); stringlist.addelement("fall"); stringlist.addelement("winter"); Java Programming: Program Design Including Data Structures 33 11

12 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 Java Programming: Program Design Including Data Structures 34 Programming Example: Election Results 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 Java Programming: Program Design Including Data Structures 35 Programming Example: Election Results (Solution) The solution includes: Reading the candidates names into the array candidatename Two-dimensional array consisting of votes by region Array consisting of the total votes, parallel to the candidatename array Java Programming: Program Design Including Data Structures 36 12

13 Programming Example: Election Results (Solution) Sorting the array candidatesname Processing the voting data Calculating the total votes received by each candidate Outputting the results in tabular form Java Programming: Program Design Including Data Structures 37 Programming Example: Election Results Java Programming: Program Design Including Data Structures 38 Programming Example: Election Results (continued) Java Programming: Program Design Including Data Structures 39 13

14 Additional String Methods Java Programming: Program Design Including Data Structures 40 Additional String Methods (continued) Java Programming: Program Design Including Data Structures 41 Additional String Methods (continued) Java Programming: Program Design Including Data Structures 42 14

15 Additional String Methods (continued) Java Programming: Program Design Including Data Structures 43 Effects of Some String Methods Java Programming: Program Design Including Data Structures 44 Programming Example: Pig Latin Strings If string begins with a vowel, -way is appended 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 Java Programming: Program Design Including Data Structures 45 15

16 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 Java Programming: Program Design Including Data Structures 46 Programming Example: Pig Latin Strings (Sample Runs) Java Programming: Program Design Including Data Structures 47 Chapter Summary Lists Searching lists: Sequential searching Sequential searching on an order list Binary search Sorting lists: Bubble sort Selection sort Insertion sort Java Programming: Program Design Including Data Structures 48 16

17 Chapter Summary (continued) Programming examples The class Vector Members of the class Vector The class String Additional methods of the class String Java Programming: Program Design Including Data Structures 49 17