Unable to get error message in Java Program

Question

I am solving a problem on spoj, here is the URL http://www.spoj.com/problems/FACEFRND/

But getting an error and unable to identify my mistake, code is as follows:

import java.util.ArrayList;
import java.util.Scanner;

public class Facefrnd {

    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        ArrayList<Integer> f = new ArrayList<Integer>();
        ArrayList<Integer> fof = new ArrayList<Integer>();
        int n, t, id, m;
        n = sc.nextInt();
        t = n;
        while(t>0){
            t--;
            id = sc.nextInt();
            m = sc.nextInt();
            f.add(id);
            if(fof.contains(id))
                fof.remove(id);
            for(int j = 0; j < m; j++){
                id = sc.nextInt();
                if(!f.contains(id))
                    fof.add(id);
            }
        }
        System.out.print(fof.size());
    }

}

Error is with sample input:

3

2334 5 1256 4323 7687 3244 5678

1256 2 2334 7687

4323 5 2334 5678 6547 9766 9543Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 1256, Size: 5

at java.util.ArrayList.rangeCheck(ArrayList.java:635)

at java.util.ArrayList.remove(ArrayList.java:474)

at sampleproject.Facefrnd.main(Facefrnd.java:22)

Answer 1

The Arraylist.remove() method for ArrayLists of type Integer defaults to the remove that takes an index. In order to remove it, you can do:

fof.remove(new Integer(id));

This ensures that the remove(Object o) method is called instead.

Sample Code:

ArrayList<Integer> test = new ArrayList<Integer>();                          
test.add(123);                                                               
test.remove(new Integer(123));                                               
System.out.println(test.size());   

This will print "0".