Remove and add the items from one list to another at the specified index

Question

I have two ArrayList s :

ArrayList a = [1,2,3,4,5,6,7,8,9,10,11.......100]
ArrayList b = [a1,a2,a3,a4,a5,a6,a7,a8,a9,a10.......a100]

remove the every 5th and 6th elements of ArrayList a like 5,6 11,12 and so on and to the ArrayList b.

and also remove every 6th and 7th item of ArrayList b like a6,a7,a13,a14 so on and add it to ArrayList a.

so my output ArrayList s would be.

 ArrayList a = [1,2,3,4,a6,a7,7,8,9,10,a13,a14,13,14,15,16,a20,a21 and so on]
 ArrayList b = [a1,a2,a3,a4,a5,5,6,a8,a9,a10,a11,a12,11,12 ,a15,a16,a17,a18,a19,17,18and so on]

so how can I achieve this?

I tried it but not in an exact way.

       int highAdded = 0;
    int normalAdded = 0;
    for (Iterator<BaseItem> iterator = mItems.iterator(); iterator.hasNext(); ) {
        BaseItem itemtype = iterator.next();
        if (itemtype.isHighlightPost()) {

            highAdded++;
            if (highAdded == 5) {
                normal.add(itemtype);
            } else if (highAdded == 6) {
                normal.add(itemtype);
                highAdded = 0;
            } else {
                highlighted.add(itemtype);
            }
        } else {
            normalAdded++;
            if (normalAdded == 6) {
                highlighted.add(itemtype);
            } else if (normalAdded == 7) {
                highlighted.add(itemtype);
                normalAdded = 0;
            } else {
                normal.add(itemtype);
            }
        }

    }

Thanks

Answer 1

this should do the job, note that here there is no removal, but it does replacements. Ensure that N is set so that no list sizes are exceeded.

/** Multiplier for a-list index */
private final static int M_A = 6;
/** Multiplier for b-list index */
private final static int M_B = 7;

{
   // ...
   final int n = Math.min( a.size() / M_A, b.size() / M_B );
   for ( int i = 1; i <= n; i++ ) {
      exchange( a, b, i * M_A - 2, i * M_B - 2 );
      exchange( a, b, i * M_A - 1, i * M_B - 1 );
   }
   // ...
}

private <T> void exchange( List<T> a, List<T> b, int aIndex, int bIndex ) {
   T elem1 = a.get( aIndex );
   a.set( aIndex, b.get( bIndex ) );
   b.set( bIndex, elem1 );
}

(edited to match 'specification' for index counters) (edit 2, added also computation of n)

Answer 2

you can done this through set() method of arraylist

public void arraylistproblem()
{
    ArrayList<String> a=new ArrayList<>();
    for(int i=1;i<=100;i++)
    {
        a.add(""+i);
    }

    ArrayList<String> b=new ArrayList<>();
    for(int j=1;j<=100;j++)
    {
        b.add("a"+j);
    }

    System.out.print("Arraylist a = ");
    for(int i1=0;i1<a.size();i1++)
    {
        System.out.print(a.get(i1)+",");
    }
    System.out.print("Arraylist b = ");
    for(int i1=0;i1<b.size();i1++)
    {
        System.out.print(b.get(i1) + ",");
    }

    int aIndex=4;
    int bIndex=5;
    for(int i=0;i<a.size();i++)
    {

        if(aIndex>=a.size() || bIndex>=b.size())
            break;

        String aTemp1=a.get(aIndex);
        String bTemp1=b.get(bIndex);

        /**
         * swap the values .. 5th of a-arraylist and 6th of b-arraylist
         */
        a.set(aIndex++, bTemp1);
        b.set(bIndex++, aTemp1);

        String aTemp2=a.get(aIndex);
        String bTemp2=b.get(bIndex);

        /**
         * swap the values .. 6th of a-arraylist and 7th of b-arraylist
         */
        a.set(aIndex, bTemp2);
        b.set(bIndex, aTemp2);

        aIndex=aIndex+5;
        bIndex=bIndex+6;
    }

    System.out.print("Arraylist a = ");
    for(int i1=0;i1<a.size();i1++)
    {
        System.out.print(a.get(i1)+",");
    }
    System.out.print("Arraylist b = ");
    for(int i1=0;i1<b.size();i1++)
    {
        System.out.print(b.get(i1)+",");
    }
}