Foo3.java

import java.util.*;

class Foo3{


	public static void main(String args[]){


		int[] l = {4,3,2,1};
		answer(l);


	}

	public static int answer(int[] l){



		class GenQueue<E> {
   				
   				private LinkedList<E> list = new LinkedList<E>();
			   public void enqueue(E item) {
			      list.addLast(item);
			   }
			   public E dequeue() {
			      return list.poll();
			   }
			   public boolean hasItems() {
			      return !list.isEmpty();
			   }
			   public int size() {
			      return list.size();
			   }
			   public void addItems(GenQueue<? extends E> q) {
			      while (q.hasItems())
			         list.addLast(q.dequeue());
			   }
		}

		
		Integer[] ll = new Integer[l.length];
		for(int i=0;i<l.length;i++){

			ll[i] = l[i];

		}


		Arrays.sort(ll);


		GenQueue<Integer> queue0 = new GenQueue<Integer>();
		GenQueue<Integer> queue1 = new GenQueue<Integer>();
		GenQueue<Integer> queue2 = new GenQueue<Integer>();
		
		int sum = 0;

		for( int i=0 ; i<ll.length ; i++){

			sum = sum + ll[i];

			if(ll[i] % 3 == 0){

				queue0.enqueue(ll[i]);

			}
			else{
				if(ll[i] % 3 == 1){

					queue1.enqueue(ll[i]);

				}else{

					queue2.enqueue(ll[i]);

				}
			}
		}

		if ( (sum % 3) == 1 )
   		{
        	// either remove one item from queue1
   		    if ( queue1.hasItems() )
	            queue1.dequeue();
 
        	// or remove two items from queue2
        	else
        	{
            	if ( queue2.hasItems() )
        	        queue2.dequeue();
	            else
    	            return 0;
 
            	if ( queue2.hasItems() )
                	queue2.dequeue();
            	else
            	    return 0;
        	}
        }
        else 
		if ((sum % 3) == 2)
	    {
	        // either remove one item from queue2
	        if ( queue2.hasItems() )
	            queue2.dequeue();
	 
	        // or remove two items from queue1
	        else
	        {
	            if ( queue1.hasItems() )
	                queue1.dequeue();
	            else
	                return 0;
	 
	            if ( queue1.hasItems() )
	                queue1.dequeue();
	            else
	                return 0;
	        }
	    }
    	int n = queue2.size() + queue1.size() + queue0.size() ;

    	int[] ans = new int[n];
    	
    	
    	int i=0;
    	while(queue0.hasItems()){

    		ans[i] = queue0.dequeue();
    		++i;

    	}
    	while(queue1.hasItems()){

    		ans[i] = queue1.dequeue();
    		++i;

    	}
    	while(queue2.hasItems()){

    		ans[i] = queue2.dequeue();
    		++i;

    	}

    	Arrays.sort(ans);

    	
    	int ret = 0;
    	for(int j=i-1 ; j>=0 ; j--){


    		ret = ret * 10;
    		ret += ans[j];

    	}
    	System.out.println(ret);
    	return ret;
	}

}