INFO 16029

Problem Solving and

Programming Logic

INFO 16029

Problem Solving and

Programming Logic

Arrays

Sorting

04/19/23 Wendi Jollymore, ACES 2

Array ConceptsArray Concepts

Index

data 0

1

2

3

4

n - 2

n - 1

Array

Elementlength = n

04/19/23 Wendi Jollymore, ACES 3

Array ConceptsArray Concepts

Why do we use them?See example in notes

04/19/23 Wendi Jollymore, ACES 4

Coding ArraysCoding Arrays

Define the type and lengthPseudocode:

integer arrayName[n]Assumes 0-based array

First index is 0, last index is n-1

Java:int[] arrayName = new int[n];

04/19/23 Wendi Jollymore, ACES 5

Coding ArraysCoding Arrays

Accessing elements:Pseudocode:

Print numbers[i]firstNames[i] = “Fred”

Java:System.out.println(numbers[i]);firstNames[i] = “Fred”;

04/19/23 Wendi Jollymore, ACES 6

Coding ArraysCoding Arrays

Fill an array with values:

Print and calculate average:

integer numbers[10] For counter = 0 to 9

Print "Enter number ", counter+1 Get numbers[counter]

For counter = 0 to 9 Print numbers[counter] Add numbers[counter] to total

Print total / 10

04/19/23 Wendi Jollymore, ACES 7

ExercisesExercises

Try the three exercises in the notes:A string array called names[] with 25 elements contains the last names of all the salespeople in a company. Write the pseudocode to ask the user for a salesperson's name, then sequentially search the array for that person's name. For all matches in the list, display the index number. Otherwise, display a "not found" message.

04/19/23 Wendi Jollymore, ACES 8

ExercisesExercises

Rewrite the pseudocode at the beginning of this lesson using an array for the grades, but record grades for 6 courses.Ask the user to enter five numbers. Store the numbers in an array and then determine if the numbers were entered in ascending order. Display a message indicating whether they are sorted or not.

04/19/23 Wendi Jollymore, ACES 9

Parallel ArraysParallel Arrays

For grades exampleWhat if we wanted to display course code?See code in notes

PROG10082

INFO16029

MATH26507

SYST16529

SYST10049

87.0

88.2

92.5

79.8

85.7

String[] courses float[] grades0

1

2

3

4

index

04/19/23 Wendi Jollymore, ACES 10

ExerciseExercise

A program calculates the total revenue for various items sold in a kiosk. There are 2 arrays: price[] and quantity[]. The price[] array contains the prices of 25 items, and the quantity[] array contains the quantity[] of each of the 25 items sold. For example, price[3] contains the price of item 4 and quantity[3] contains the number of item 4's sold.Create a third array, revenue[] that is parallel to price[] and quantity[]. Fill this array with the total revenue of each of the 25 items. Revenue = price * quantity sold.

04/19/23 Wendi Jollymore, ACES 11

Sorting ArraysSorting Arrays

Many different sort algorithmsChoice depends on size of listBubble Sort

Simplest, easiest to learnGood for small lists (n <= 28)Demo…

04/19/23 Wendi Jollymore, ACES 12

Sorting ArraysSorting Arrays

Bubble Sort summary:Number of passes: n – 1Each pass puts one more element in its correct positionEach pass has x – 1 comparisons

Let x = # of unsorted elements

Maximum number of comparisons:The sum of the values from 1 to n-1

n-1

∑ i i=1

04/19/23 Wendi Jollymore, ACES 13

ExercisesExercises

Sort these in ascending order:64 33 25 51 19 40

Try sorting in descending order

For an array with 6 elements:How many passes?How many comparisons in total?

For an array with 7 elements?

04/19/23 Wendi Jollymore, ACES 14

Bubble Sort LogicBubble Sort Logic

Explained in the notesThe main action taking place is swapping

E.g. if a pair of items are out of order, swap!

If grades[currEl] > grades[currEl+ 1] Then tempGrade = grades[currEl] grades[currEl] = grades[currEl + 1]

grades[currEl + 1] = tempGradeEnd If

04/19/23 Wendi Jollymore, ACES 15

Bubble Sort LogicBubble Sort Logic

One Pass:

numComparisons = numberElements - 1 currEl= 0 While currEl < numComparisons If grades[currEl] > grades[currEl + 1] Then

tempGrade = grades[currEl] grades[currEl] = grades[currEl + 1]

grades[currEl + 1] = tempGrade End If Add 1 to currEl

Bubble Sort LogicBubble Sort Logic

All Passes:

04/19/23 Wendi Jollymore, ACES 16

passNumber = 1 numComparisons = numberElements - 1 While passNumber <= numberElements – 1 currEl= 0 While currEl < numComparisons If grades[currEl] > grades[currEl + 1] Then

tempGrade = grades[currEl] grades[currEl] = grades[currEl + 1]

grades[currEl + 1] = tempGrade End If Add 1 to currEl Subtract 1 from numComparisons Add 1 to passNumber

Other Sort AlgorithmsOther Sort Algorithms

Sorting is usually part of a larger course in Data StructuresSee links in notes for more sort algorithms

04/19/23 Wendi Jollymore, ACES 17