Java lists issue

Question

I'm trying to write a method that receives a List of strings, and returns subsets that contains n elements. Here is my code:

import Pack;
import java.util.List;
import java.util.ArrayList;

public class Testtt{
    public static void main(String[] args) {
        List<String> input = new ArrayList<String>();
        input.add("a");
        input.add("b");
        input.add("c");
        input.add("d");
        input.add("e");

        System.out.println(subset(input, 3));
    }

    public static List<List<String>> subset( List<String> inputlist, int n) {
        List<List<String>> output = new ArrayList<List<String>>();
        List<String> temp = new ArrayList<String>();

        for (int i = 0; i < n; i++) {
                temp = inputlist;
                System.out.println("Temp = " +temp);
                temp.remove(i);
                output.add(temp);
        }

        return output;
    }
}

Output was containing only 2 elements i decided to debug and this is the console output:

Temp = [a, b, c, d, e]
Temp = [b, c, d, e]
Temp = [b, d, e]
[[b, d], [b, d], [b, d]]

I've written temp = list at the beginning of the loop but it stays the same. Why this is happening?

Welcome to StackOverflow. Questions asking about problems in the code must include the code, not a link to an external site like pastebin. If the code is too long, you are supposed to cut it down to only the essential part that shows the problem. Please read how to ask and how to create an MCVE. — RealSkeptic
– RealSkeptic, Commented Aug 1, 2015 at 8:58

Shriram · Accepted Answer · 2015-08-01 08:59:00Z

1

for (int i = 0; i < n; i++) {
                        temp = inputlist;
                        System.out.println("Temp = " +temp);
                        temp.remove(i);
                        output.add(temp);
                }

Here you are removing an element from temp arraylist and adding it to output arraylist. As of now you are keeping the reference of temp and making the removal on the same temp arraylist will lead to the output which you have shown. As per your program the shown output is correct. If you want it temp ouput should be storead in output arralist just create new instance of array list and store it inside output.

answered Aug 1, 2015 at 8:59

Shriram

4,4318 gold badges43 silver badges69 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Sneftel · Accepted Answer · 2015-08-01 09:47:03Z

1

I can't understand the expected result here. But there are two fundamental mistakes:

you modify the input list
within a indexed loop you remove an element from a list. this will result in skipping elements through the iteration.

That is why this code remove a and c and e , but not b and d.

edited Aug 1, 2015 at 9:47

Sneftel

41.9k13 gold badges78 silver badges112 bronze badges

answered Aug 1, 2015 at 9:36

hunter

4,2131 gold badge18 silver badges19 bronze badges

Collectives™ on Stack Overflow

Java lists issue

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related