How should I change in get method without calling getList() of Deque? [closed]

Question

Closed. This question needs details or clarity. It is not currently accepting answers.

---

Want to improve this question? Add details and clarify the problem by editing this post.

Closed 5 years ago.

Improve this question

import java.util.List;
import java.util.ArrayList;

public class Test {

    /**
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        Deque queue = new Deque();

        int random = (int)(Math.random() * 100);

        queue.addLast(10);
        queue.addLast(20);
        queue.addLast(random);
        queue.addLast(40);
        queue.addLast(50);

        for(int i = 0; i < 2; i++) {

            assertTrue(get(queue, 0) == 10);
            assertTrue(get(queue, 1) == 20);
            assertTrue(get(queue, 2) == random);
            assertTrue(get(queue, 4) == 50);
            assertTrue(get(queue, 3) == 40);

            try {
                System.out.println(get(queue, 5));
                assertTrue(false);
            } catch(Exception e) {
                assertTrue(true);
            }
        }       
    }

    public static void assertTrue(boolean v) {
        if(!v) {
            Thread.dumpStack();
            System.exit(0);
        }
    }


    public static int get(Deque queue, int index) throws Exception 
    {     
        // 1) Only fill in your code in this method
        // 2) Do not modify anything else
        // 3) Use of 'new' keyword is not allowed
        // 4) Do not use reflection
        // 5) Do not use string concatenation

        return queue.getList().get(index);      
    }
}

class Deque {
    private List<Integer> items;

    public Deque() {
        items = new ArrayList<Integer>();
    }

    public void addFirst(int item) {
        items.add(0, item);
    }

    public void addLast(int item) {
        items.add(item);
    }

    public int removeFirst() {
        if(isEmpty()) throw new RuntimeException();
        return items.remove(0);
    }

    public int removeLast() {
        if(isEmpty()) throw new RuntimeException();
        return items.remove(items.size() - 1);
    }

    public boolean isEmpty() {
        return items.size() == 0;
    }

    public List<Integer> getList()
    {
        return items;       
    }
}

Thanks

~July

Answer 1

You can use recursion to remove index-1 elements from the beginning of the queue, store the the first element and then, as you are unwinding the recursion, put removed elements back on the queue:

public static int get(Deque queue, int index) throws Exception {
    int tmp = queue.removeFirst();
    try {
        if (index == 0) {
            return tmp;
        } else {
            return get(queue, index - 1);
        }
    } finally {
        queue.addFirst(tmp);
    }
}