Algorithm course: Output of int sort and method to sort Strings

Question

My assignment asks me to make a TV show program, where I can input shows, delete, modify and sort them. What I'm stuck on is the sorting part. With the show, it asks for the name, day a new episode premieres, and time. Those are the keys I need to sort it by.

The program prompts the user to input one of those keys, then the program needs to sort (sorting by day will sort alphabetically).

I made a class and used an array. Here is the class:

public class showInfo 
{
String name;
String day; 
int time;     
}

And the method to sort by time in the code:

public static void intSort()
{
    int min;
    for (int i = 0; i < arr.length; i++) 
    {

        // Assume first element is min
        min = i;
        for (int j = i+1; j < arr.length; j++) 
        {
            if (arr[j].time < arr[min].time) 
            {
                min = j;
            }
        }

        if (min != i) 
        {
            int temp = arr[i].time;
            arr[i].time = arr[min].time;
            arr[min].time = temp;
        }
    }
    System.out.println("TV Shows by Time");
    for(int i = 0; i < arr.length; i++)
    {
        System.out.println(arr[i].name + " - " + arr[i].day + " - " + arr[i].time + " hours");
    }
}

When I call it and output it in the main, it only shows "TV Shows by Time" and not the list. Why is this?

Also, I need to make ONE method that I will be able to use to sort both the day AND the name (both Strings). How can I do this without using those specific arrays (arr[i].name, arr[i].day) in the method?

Any help would be greatly appreciated! Thanks in advance!

Answer 1

Why not you use a Collection for this sort of a thingy to work. Moreover, in your added example, you are simply changing one attribute of a given object, while sorting, though you not changing the position of the object as a whole, inside the given list.

Create a List which will contain the references of all the Shows, now compare each attribute of one Show with another, in the List. Once the algorithm feels like, that swapping needs to be done, simply pick the reference from the List, save it in a temp variable, replace it with a new reference at this location, and set duplicate to the one stored in the temp variable. You are done, List is sorted :-)

Here is one small example for the same, for help :

import java.io.*;
import java.util.*;

public class Sorter {

    private BufferedReader input;
    private List<ShowInfo> showList;

    public Sorter() {
        showList = new ArrayList<ShowInfo>();
        input = new BufferedReader(
            new InputStreamReader((System.in)));
    }

    private void createList() throws IOException {
        for (int i = 0; i < 5; i++) {           
            System.out.format("Enter Show Name :");
            String name = input.readLine();
            System.out.format("Enter Time of the Show : ");
            int time = Integer.parseInt(input.readLine());
            ShowInfo show = new ShowInfo(name, time);
            showList.add(show);
        }
    }

    private void performTask() {
        try {
            createList();
        } catch (Exception e) {
            e.printStackTrace();
        }
        sortByTime(showList);
    }

    private void sortByTime(List<ShowInfo> showList) {
        int min;
        for (int i = 0; i < showList.size(); i++) {

            // Assume first element is min
            min = i;
            for (int j = i+1; j < showList.size(); j++) {
                if (showList.get(j).getTime() < 
                            showList.get(min).getTime()) {
                    min = j;
                }
            }

            if (min != i) {
                ShowInfo temp = showList.get(i);
                showList.set(i, showList.get(min));
                showList.set(min, temp);
            }
        }
        System.out.println("TV Shows by Time");
        for(int i = 0; i < showList.size(); i++) {
            System.out.println(showList.get(i).getName() +
                " - " + showList.get(i).getTime());
        }
    }

    public static void main(String[] args) {
        new Sorter().performTask();
    }
}

class ShowInfo {
    private String name;
    int time;

    public ShowInfo(String n, int t) {
        name = n;
        time = t;
    }

    public String getName() {
        return name;
    }

    public int getTime() {
        return time;
    }
}

EDIT 2 :

For sorting By Name you can use this function :

private void sortByName(List<ShowInfo> showList) {
    int min;
    for (int i = 0; i < showList.size(); i++) {         
        // Assume first element is min
        min = i;
        for (int j = i+1; j < showList.size(); j++) {               
            int value = (showList.get(j).getName()).compareToIgnoreCase(
                                            showList.get(min).getName());
            if (value < 0)
                min = j;
        }

        if (min != i) {
            ShowInfo temp = showList.get(i);
            showList.set(i, showList.get(min));
            showList.set(min, temp);
        }
    }
    System.out.println("TV Shows by Time");
    for(int i = 0; i < showList.size(); i++) {
        System.out.println(showList.get(i).getName() +
                      " - " + showList.get(i).getTime());
    }
}

EDIT 3 :

Added Comparable<?> Interface, to the existing class to perform sorting based on specified input. Though one can improve on the logic, by using Enumeration, though leaving it for the OP to try his/her hands on :-)

import java.io.*;
import java.util.*;

public class Sorter {

    private BufferedReader input;
    private List<ShowInfo> showList;
    private int command;

    public Sorter() {
        showList = new ArrayList<ShowInfo>();
        input = new BufferedReader(
            new InputStreamReader((System.in)));
        command = -1;
    }

    private void createList() throws IOException {
        for (int i = 0; i < 5; i++) {           
            System.out.format("Enter Show Name :");
            String name = input.readLine();
            System.out.format("Enter Time of the Show : ");
            int time = Integer.parseInt(input.readLine());
            ShowInfo show = new ShowInfo(name, time);
            showList.add(show);
        }
    }

    private void performTask() {
        try {
            createList();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.format("How would you like to sort : %n");
        System.out.format("Press 0 : By Name%n");
        System.out.format("Press 1 : By Time%n");
        try {
            command = Integer.parseInt(input.readLine());
        } catch (Exception e) {
            e.printStackTrace();
        }
        sortList(showList);
    }

    private void sortList(List<ShowInfo> showList) {
        int min;
        for (int i = 0; i < showList.size(); i++) {

            // Assume first element is min
            min = i;
            for (int j = i+1; j < showList.size(); j++) {
                showList.get(j).setValues(command);
                int value = showList.get(j).compareTo(showList.get(min));
                if (value < 0) {
                    min = j;
                }
            }

            if (min != i) {
                Collections.swap(showList, i, min);
            }
        }
        System.out.println("TV Shows by Time");
        for(int i = 0; i < showList.size(); i++) {
            System.out.println(showList.get(i).getName() +
                " - " + showList.get(i).getTime());
        }
    }   

    public static void main(String[] args) {
        new Sorter().performTask();
    }
}

class ShowInfo  implements Comparable<ShowInfo> {

    private String name;
    private int time;
    private int command;

    public ShowInfo(String n, int t) {
        name = n;
        time = t;
    }

    public String getName() {
        return name;
    }

    public int getTime() {
        return time;
    }

    public void setValues(int cmd) {
        command = cmd;
    }

    public int compareTo(ShowInfo show) {
        int lastCmp = 1;
        if (command == 0) {
            lastCmp = name.compareTo(show.name);
        } else if (command == 1) {
            if (time < show.time) {
                lastCmp = -1;
            } else if (time == show.time) {
                lastCmp = 0;
            } else if (time > show.time) {
                lastCmp = 1;
            }
        }

        return lastCmp;
    }
}

Answer 2

In this part of your code

if (min != i) {
    int temp = arr[i].time;
    arr[i].time = arr[min].time;
    arr[min].time = temp;
}

You're just changing the time when you should move the whole object instead. To fix it, the code must behave like this:

if (min != i) {
    //saving the object reference from arr[i] in a temp variable
    showInfo temp = arr[i];
    //swapping the elements
    arr[i] = arr[min];
    arr[min] = temp;
}

I̶t̶ ̶w̶o̶u̶l̶d̶ ̶b̶e̶ ̶b̶e̶t̶t̶e̶r̶ ̶t̶o̶ ̶u̶s̶e̶ ̶ Arrays#sort ̶w̶h̶e̶r̶e̶ ̶y̶o̶u̶ ̶p̶r̶o̶v̶i̶d̶e̶ ̶a̶ ̶c̶u̶s̶t̶o̶m̶ ̶̶C̶o̶m̶p̶a̶r̶a̶t̶o̶r̶̶ ̶o̶f̶ ̶t̶h̶e̶ ̶c̶l̶a̶s̶s̶ ̶b̶e̶i̶n̶g̶ ̶s̶o̶r̶t̶e̶d̶ ̶(̶i̶f̶ ̶y̶o̶u̶ ̶a̶r̶e̶ ̶a̶l̶l̶o̶w̶e̶d̶ ̶t̶o̶ ̶u̶s̶e̶ ̶t̶h̶i̶s̶ ̶a̶p̶p̶r̶o̶a̶c̶h̶)̶.̶ ̶S̶h̶o̶r̶t̶ ̶e̶x̶a̶m̶p̶l̶e̶:̶

showInfo[] showInfoArray = ...
//your array declared and filled with data
//sorting the array
Arrays.sort(showInfoArray, new Comparator<showInfo>() {
    @Override
    public int compare(showInfo showInfo1, showInfo showInfo2) {
        //write the comparison logic
        //basic implementation
        if (showInfo1.getTime() == showInfo2.getTime()) {
             return showInfo1.getName().compareTo(showInfo2.getName());
        }
        return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
    }
});
//showInfoArray will be sorted...

---

Since you have to use a custom made sorting algorithm and support different ways to sort the data, then you just have to change the way you compare your data. This mean, in your current code, change this part

if (arr[j].time < arr[min].time) {
    min = j;
}

To something more generic like

if (compare(arr[j], arr[min]) < 0) {
    min = j;
}

Where you only need to change the implementation of the compare method by the one you need. Still, it will be too complex to create and maintain a method that can support different ways to compare the data. So the best option seems to be a Comparator<showInfo>, making your code look like this:

if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
    min = j;
}

where the showInfoComparator holds the logic to compare the elements. Now your intSort would become into something more generic:

public static void genericSort(Comparator<showInfo> showInfoComparator) {
    //your current implementation with few modifications
    //...
    //using the comparator to find the minimum element
    if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
        min = j;
    }
    //...
    //swapping the elements directly in the array instead of swapping part of the data
    if (min != i) {
        int temp = arr[i].time;
        arr[i].time = arr[min].time;
        arr[min].time = temp;
    }
    //...
}

Now, you just have to write a set of Comparator<showInfo> implementations that supports your custom criteria. For example, here's one that compares showInfo instances using the time field:

public class ShowInfoTimeComparator implements Comparator<showInfo> {
    @Override
    public int compare(showInfo showInfo1, showInfo showInfo2) {
        //write the comparison logic
        return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
    }
}

Another comparator that uses the name field:

public class ShowInfoNameComparator implements Comparator<showInfo> {
    @Override
    public int compare(showInfo showInfo1, showInfo showInfo2) {
        //write the comparison logic
        return showInfo1.getName().compareTo(showInfo2.getName());
    }
}

Now in your code you can call it like this¹:

if (*compare by time*) {
    genericSort(showInfoArray, new ShowInfoTimeComparator());
}
if (*compare by name*) {
    genericSort(showInfoArray, new ShowInfoNameComparator());
}
if (*another custom rule*) {
    genericSort(showInfoArray, new ShowInfoAnotherCustomRuleComparator());
}

where now you can implement a custom rule like compare showInfo objects using two or more fields. Taking as example your name and day fields (as stated in the question):

public class ShowInfoNameAndDayComparator implements Comparator<showInfo> {
    @Override
    public int compare(showInfo showInfo1, showInfo showInfo2) {
        //write the comparison logic
        int nameComparisonResult = showInfo1.getName().compareTo(showInfo2.getName());
        if (nameComparisonResult == 0) {
            return showInfo1.getDay().compareTo(showInfo2.getDay());
        }
        return nameComparisonResult;
    }
}

¹: There are other ways to solve this instead using lot of if statements, but looks like that's outside the question scope. If not, edit the question and add it to show another ways to solve this.

---

Other tips for your current code:

• Declare the names of the classes using CamelCase, where the first letter of the class name is Upper Case, so your showInfo class must be renamed to ShowInfo.

• To access to the fields of a class, use proper getters and setters instead of marking the fields as public or leaving the with default scope. This mean, your ShowInfo class should become into:

  public class ShowInfo {
      private String name;
      private String day; 
      private int time;
      public String getName() {
          return this.name;
      }
      public void setName(String name) {
          this.name = name;
      }
      //similar for other fields in the class
  }
  

Answer 3

Use selection sort algorithm which is easy to implement,

for (int i = 0; i < arr.length; i++)
        {
            for (int j = i + 1; j < arr.length; j++)
            {
                if (arr[i].time > arr[j].time) // Here ur code that which should be compare
                {
                    ShowInfo temp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = temp;
                }
            }
        }

no need to check min element. go through this wiki http://en.wikipedia.org/wiki/Selection_sort