LeetCode225. 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

Notes:

• You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.

---

思路:用队列去模拟栈,不过python没有队列,所以用list模拟.注意栈的pop()和top()都应该是数组最后一个元素.

class MyStack(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.q=[]

    def push(self, x):
        """
        Push element x onto stack.
        :type x: int
        :rtype: void
        """
        self.q.append(x)
        

    def pop(self):
        """
        Removes the element on top of the stack and returns that element.
        :rtype: int
        """
        return self.q.pop(-1)
        
    def top(self):
        """
        Get the top element.
        :rtype: int
        """
        return self.q[-1]

    def empty(self):
        """
        Returns whether the stack is empty.
        :rtype: bool
        """
        return not self.q