[LC] 225. Implement Stack using Queues

Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

Example:

MyStack stack = new MyStack();

stack.push(1);
stack.push(2);
stack.top();   // returns 2
stack.pop();   // returns 2
stack.empty(); // returns false

class MyStack:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        from collections import deque
        self.queue = deque()

    def push(self, x: int) -> None:
        """
        Push element x onto stack.
        """
        self.queue.append(x)
        for i in range(len(self.queue) - 1):
            self.queue.append(self.queue.popleft())

    def pop(self) -> int:
        """
        Removes the element on top of the stack and returns that element.
        """
        return self.queue.popleft()

    def top(self) -> int:
        """
        Get the top element.
        """
        return self.queue[0]

    def empty(self) -> bool:
        """
        Returns whether the stack is empty.
        """
        return not self.queue

# Your MyStack object will be instantiated and called as such:
# obj = MyStack()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.empty()

class MyStack {

    /** Initialize your data structure here. */
    Queue<Integer> queue;
    public MyStack() {
        queue = new LinkedList<>();
    }

    /** Push element x onto stack. */
    public void push(int x) {
        queue.offer(x);
        for (int i = 0; i < queue.size() - 1; i++) {
            queue.offer(queue.poll());
        }
    }

    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return queue.poll();
    }

    /** Get the top element. */
    public int top() {
        return queue.peek();
    }

    /** Returns whether the stack is empty. */
    public boolean empty() {
        return queue.isEmpty();
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */