CareerCup

Q1 and Q2

For O(1) push() and O(N) pop():

1. Enqueue into Q1.
2. If pop, check size of Q1, if size > 1, dequeue into Q2 until size == 1
3. Dequeue from Q1, return result
4. Switch back and forth

For O(N) push() and O(1) pop():

1. push() -> Enqueue into Q1
2. push() -> Enqueue into Q2, and Dequeue Q1 into Q2
3. repeat back and forth
4. pop() -> Dequeue from the Q that has element

public class StackWithQueue
    { 
        private Queue<char> Q1= new Queue<char>();
        private Queue<char> Q2 = new Queue<char>();

        public void Push(char ch)
        {
            if (Q1.Count == 0)
            {
                Q1.Enqueue(ch);
                MoveQItems(Q2,Q1); // Move items from Q2 to Q1
            }
            else
            {
                Q2.Enqueue(ch);
                MoveQItems(Q1, Q2);
            }
        }

        public char Pop()
        {
            if (Q1.Count != 0)
            {
                return Q1.Dequeue();
            }
            else if (Q2.Count != 0)
            {
                return Q2.Dequeue();
            }
            return ' '; 
        }

        private void MoveQItems(Queue<char> a, Queue<char> b)
        {
            while (a.Count != 0)
            {
                b.Enqueue(a.Dequeue());
            }
        }

}

PushQueue, PopQueue.
1. starting, both empty.
2. push operation done by "PushQueue.push()"
3. pop operation done by

int t = 0;
while (t < (PushQueue.size() - 1)) {
    PopQueue.push(PushQueue.pop());
}
return PushQueue.pop();

4. swap PushQueue and PopQueue.