LeetCode/225. ImplementStackUsingQueue LeetCode/232. ImplementQueueUsingStack

Summary

Basically both are asking the same question. Can you logically think about this.
Graphically imagine about this is a good way to solve this. Think about you have [1,2,3,4,5].
Think about both solution that you have Two Queue when implementing stack, and Two Stack when Implementing queue.

Solutions

My Solution

  • Implement stack using queue.
public class MyBestStack
{
    Queue<int> qStack = new Queue<int>();

    /** Push element x onto stack. */
    public void Push(int x)
    {
        qStack.Enqueue(x);
        for (int i = 0; i < qStack.Count - 1; i++)
            qStack.Enqueue(qStack.Dequeue());
    }

    // Removes the element on top of the stack.
    public int Pop()
    {
        return qStack.Dequeue();
    }

    // Get the top element.
    public int Top()
    {
        return qStack.Count > 0 ? qStack.Peek() : 0;
    }

    // Return whether the stack is empty.
    public bool Empty()
    {
        return qStack.Count == 0;
    }
}

  • Implement queue using stack.

    public class MyBestQueue
{
Stack<int> sQueue = new Stack<int>();
Stack<int> stackHelper = new Stack<int>();

/** Push element x to the back of queue. */
public void Push(int x)
{
    sQueue.Push(x);
}

/** Removes the element from in front of queue and returns that element. */
public int Pop()
{
    Peek();
    return stackHelper.Pop();
}

/** Get the front element. */
public int Peek()
{
    if (stackHelper.Count != 0) return stackHelper.Peek();
    while (sQueue.Count != 0) stackHelper.Push(sQueue.Pop());
    return stackHelper.Peek();
}

/** Returns whether the queue is empty. */
public bool Empty()
{
    return sQueue.Count == 0 && stackHelper.Count == 0;
}
}
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