Selection Sort using ArrayList

Question

I'm trying to code a selection sort using ArrayList. My program requires me to create an array of size 20 and populate it with random integers between 1 and 1000 (no user input or hard code). The output will require displaying the original unsorted list of integers, and displaying each pass of the sorting algorithm on a separate line.

I tried creating a method for the selection sort, so that's where I'm stuck because I'm not sure how to implement the code into my main method.

An example of how I want my output to come out as is shown below (although it only shows 5 integers when I'm trying to do 20):

Unsorted list: 3 68 298 290 1
Pass 1: 1 68 298 290 3
Pass 2: 1 3 298 290 68
Pass 3: 1 3 68 290 298
Pass 4: 1 3 68 290 298

// Used to capture keyboard input
import java.util.*;

// Our class called SelectionSort
public class SelectionSort {

// Create doSelectionSort method 
public static int[] doSelectionSort(int[] arr) {
    for (int i = 0; i < arr.length - 1; i++) {
        int pos = i;
        // find position of smallest num between (i + 1)th element and last element
        for (int j = i + 1; j <= arr.length; j++) {
            if (arr[j] < arr[pos])
                pos = j;

            // Swap min (smallest num) to current position on array
            int min = arr[pos];
            arr[pos] = arr[i];
            arr[i] = min;
        }
    }
    return arr;
}

// Main method
public static void main(String[] args) {
    ArrayList<Integer> array = new ArrayList<Integer>(); // Declare and instantiate a new ArrayList object
    Scanner userChoice = new Scanner(System.in); // User input for quitting program
    String choice = ""; // Will hold user choice to quit program
    boolean inputFlag = false; // True if input is valid, false otherwise

    // Repeat program until user chooses to quit
    while (inputFlag = true) {
        System.out.print("\nWould you like to continue the program? (Y/N): ");
        choice = userChoice.nextLine();
        if (choice.equalsIgnoreCase("Y")) {
            try {
                /* Create an array of size 20 and populate it with random integers between 1 and 1000.
                Do not ask user for the numbers and do not hard code them */
                for (int i = 0; i < 20; i++) {
                    int integer = (int)(1000.0 * Math.random());
                    array.add(integer);
                }
                System.out.print("\nUNSORTED LIST: ");

                //Display the 20 size of the unsorted ArrayList 
                for (int i = 0; i < array.size() - 1; i++) {
                    System.out.print(array.get(i) + ", ");
                }
                // Shows very last integer with a period
                System.out.print(array.get(array.size() - 1) + "."); 
                System.out.println();
            }

            catch (IndexOutOfBoundsException e) {
                System.out.println("\nThere is an out of bounds error in the ArrayList.");
            }
            // Display each pass of the sorting algorithm on a separate line
            for (int i = 1; i < array.size(); i++) {
                System.out.print("PASS " + i + ": ");
                for (int arr2:array) {
                    System.out.print(arr2 + ", ");
                }
                System.out.print(array.get(array.size() - 1) + ".\n");
            }
        array.clear();
        }
        else if (choice.equalsIgnoreCase("N")) {
            break;
        }
        // Error message when inputting anything other than Y/N
        else { 
            System.out.println("\nERROR. Only Y, y, N, or n may be inputted.");
            System.out.println("Please try again.");
        }
    }
}
}

I'm also having trouble removing the last number from each passing because it's being displayed twice.. have any idea what I should do?

Sorry for the noob-ness of my coding, I'm still trying to understand it.

L. Kolar · Accepted Answer · 2017-01-31 10:53:35Z

I fixed your code, it should work now.

// Used to capture keyboard input
import java.util.*;

// Our class called SelectionSort
public class SelectionSort {

    // Create doSelectionSort method 
    public static void doSelectionSort(ArrayList<Integer> arr) {
        for (int i = 0; i < arr.size(); i++) {
            // find position of smallest num between (i + 1)th element and last element
            int pos = i;
            for (int j = i; j < arr.size(); j++) {
                if (arr.get(j) < arr.get(pos))
                    pos = j;
            }
            // Swap min (smallest num) to current position on array
            int min = arr.get(pos);
            arr.set(pos, arr.get(i));
            arr.set(i, min);
            printOut(i + 1, arr);
        }
    }

    private static void printOut(int pass, ArrayList<Integer> array) {
        System.out.print("PASS " + pass + ": ");
        for (int i = 0; i < array.size() - 1; i++) {
            System.out.print(array.get(i) + ", ");
        }
        // Shows very last integer with a period
        System.out.print(array.get(array.size() - 1) + "."); 
        System.out.println();
    }

    // Main method
    public static void main(String[] args) {
        ArrayList<Integer> array = new ArrayList<Integer>(); // Declare and instantiate a new ArrayList object
        Scanner userChoice = new Scanner(System.in); // User input for quitting program
        String choice = ""; // Will hold user choice to quit program
        boolean inputFlag = false; // True if input is valid, false otherwise

        // Repeat program until user chooses to quit
        while (inputFlag = true) {
            System.out.print("\nWould you like to continue the program? (Y/N): ");
            choice = userChoice.nextLine();
            if (choice.equalsIgnoreCase("Y")) {
                try {
                    /* Create an array of size 20 and populate it with random integers between 1 and 1000.
                    Do not ask user for the numbers and do not hard code them */
                    for (int i = 0; i < 20; i++) {
                        int integer = (int)(1000.0 * Math.random());
                        array.add(integer);
                    }
                    System.out.print("\nUNSORTED LIST: ");

                    //Display the 20 size of the unsorted ArrayList 
                    for (int i = 0; i < array.size() - 1; i++) {
                        System.out.print(array.get(i) + ", ");
                    }
                    // Shows very last integer with a period
                    System.out.print(array.get(array.size() - 1) + "."); 
                    System.out.println();
                    doSelectionSort(array);
                }

                catch (IndexOutOfBoundsException e) {
                    System.out.println("\nThere is an out of bounds error in the ArrayList.");
                }
            }
            else if (choice.equalsIgnoreCase("N")) {
                break;
            }
            // Error message when inputting anything other than Y/N
            else { 
                System.out.println("\nERROR. Only Y, y, N, or n may be inputted.");
                System.out.println("Please try again.");
            }
        }
    }
}

Pablo Lozano · Accepted Answer · 2017-01-31 10:51:40Z

0

Your method doSelectionSort seems ok, but it does the whole sorting. If you want to show each iteration you just need to add a line:

public static int[] doSelectionSort(int[] arr) {
    for (int i = 0; i < arr.length - 1; i++) {
        int pos = i;
        // find position of smallest num between (i + 1)th element and last element
        for (int j = i + 1; j <= arr.length; j++) {
            if (arr[j] < arr[pos])
                pos = j;

            // Swap min (smallest num) to current position on array
            int min = arr[pos];
            arr[pos] = arr[i];
            arr[i] = min;
        }
        System.out.println("Pass "+pos+" : "+arr);
    }
    return arr;
}

answered Jan 31, 2017 at 10:51

Pablo Lozano

10.4k2 gold badges43 silver badges64 bronze badges

Collectives™ on Stack Overflow

Selection Sort using ArrayList

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related