CODEWITHSUNDEEP
javaarraysarraylist
user3137376
user3137376

Reputation: 1527

arraylist.remove not working properly

I have a sorted array of integers and want to remove the duplicates, I wrote the following code

package practice;
import java.util.*;

public class pb1 {

public static void removeDup(int[] theArray){       

    ArrayList<Integer> hold=new ArrayList<Integer>();


    for(int i=0;i<theArray.length-1;i++){


            hold.add(theArray[i]);

            //System.out.println(hold);

}
    for(int i=0;i<hold.size()-1;i++){
        if(hold.get(i)==hold.get(i+1)){
            hold.remove(i);
        }

    }
    System.out.println(hold);
}


public static void main(String[]args){
    int[] now={1,1,2,2,3,4,4,4,5,5,5,5};
    removeDup(now);



}

}

trying to delete the duplicates using the arraylist.remove method, but I can still see duplicates in my printed arraylist. I dont know why, pls can someone help me? thanks

Upvotes: 0

Views: 275

Answers (4)

user2710786
user2710786

Reputation: 41

Try this: 

for (int i = 0; i < theArray.length - 1; i++) {

           if (!hold.contains(theArray[i]))

                hold.add(theArray[i]);

}

System.out.println(hold);

Upvotes: 0

Parvez
Parvez

Reputation: 641

Why do you want to manually remove duplicates? You can copy list to set to remove duplicates and then copy from set to list again. Something like this

ArrayList aList = new ArrayList();
LinkedHashSet link = new LinkedHashSet();
link.addAll(aList);
aList.clear();
aList.addAll(link);

Upvotes: 0

Azar
Azar

Reputation: 1106

An alternative solution. This takes advantage of the fact that a Set does not allow duplicate entries, and greatly simplifies your code.

public class pb1 
{

public static void removeDup(int[] theArray)
{       
    Set<Integer> hold=new TreeSet<Integer>();
    for(int i=0;i<theArray.length-1;i++)
    {
        hold.add(theArray[i]);
    }
    System.out.println(hold);
}


public static void main(String[]args)
    {
     int[] now={1,1,2,2,3,4,4,4,5,5,5,5};
     removeDup(now);
    }
}

Output:

[1, 2, 3, 4, 5]

Upvotes: 1

user2422457
user2422457

Reputation:

Iterate backwards. Deleting items forward will delete the current element THEN increment the counter/index thus skipping possible duplicates. Replace your loop with: 

for(int i = hold.size() - 1; i >= 1;i--){
    if(hold.get(i)==hold.get(i - 1)){
        hold.remove(i);
    }
}

EDIT: Your code fails at the three consecutive 4's When your index is at the first 4:

{1,1,2,2,3,>4,4,4,5,5,5,5}

it checks the next element. It deletes the current element because it sees a 4 ahead of it BUT, this is where the bug comes in. 

{1,1,2,2,3,4,>4,5,5,5,5}

Upon deletion of the first 4, the succeeding array elements MOVE BACK and then you INCREMENT your counter thus skipping the other 4. Ergo, duplicates.

Upvotes: 0

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