Remove duplicate items in arraylist

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I have below question

Quote:
You are given the following sequence of numbers,
1, 652 ,5, 15, 385, 4 , 55, 666, 13, 2, 4658, 9, 55, -588, 10, 1083, 17 ,4.
You can remove the duplicate numbers by only using For loop and ArrayList .

And this is my output

Before remove : [-588, 1, 2, 4, 4, 5, 9, 10, 13, 15, 17, 55, 55, 385, 652, 666, 1083, 4658]
[-588, 2, 4, 9, 13, 17, 55, 652, 1083]

Some items are removed.

Edit
After I remove the sort method, my output as below

Before remove : [1, 652, 5, 15, 385, 4, 55, 666, 13, 2, 4658, 9, 55, -588, 10, 1083, 17, 4]
[1, 5, 385, 55, 13, 4658, -588, 1083, 4]

What I have tried:

public class Ex {
    public static void main(String[] args) {

        ArrayList list = new ArrayList();
        list.add(1);
        list.add(652);
        list.add(5);
        list.add(15);
        list.add(385);
        list.add(4);
        list.add(55);
        list.add(666);
        list.add(13);
        list.add(2);
        list.add(4658);
        list.add(9);
        list.add(55);
        list.add(-588);
        list.add(10);
        list.add(1083);
        list.add(17);
        list.add(4);

        Collections.sort(list);

        System.out.println("Before remove : " + list);

        for (int i = 0; i < list.size(); i++) {
            for (int j = 1; j < list.size(); j++) {
                if (list.get(i) == list.get(j)) {
                    list.remove(j);
                }
            }
        }
        System.out.println(list);
    }
}

Posted 22-Oct-18 7:11am

wseng

Updated 22-Oct-18 22:13pm

v4

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Comments

Richard MacCutchan 23-Oct-18 4:26am

The problem arises because you are removing elements from the list within a loop that depends on list.size. So whenever you remove an item the number of elements is one less that the loop is expecting, so you will get the wrong results.

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CPallini · Accepted Answer · 2018-10-22T07:33:00

You cannot use the sort method, the requirements don't allow it.
On the other hand you may use the for statement: two nested loops would do the trick.

[Update]

You have to carefully read the documentation[^]: 'Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices).'
So, after a item removal, you have to deal with the new indices.
Moreover:

The outer loop should stop at (size()-1).
The inner loop should start at (i+1).

To summarize, try:

Java

// ...

System.out.println("Before remove : " + list);

for (int i = 0; i < list.size()-1; ++i)
{
    for (int j = i+1; j < list.size(); ++j)
    {
        if (list.get(i) == list.get(j))
        {
            list.remove(j);
            --j; //deal with shifted indices
        }
    }
}
System.out.println(list);

[/Update]