L232 implement-queue-using-stacks.md

implement-queue-using-stacks

Implement the following operations of a queue using stacks.

push(x) -- Push element x to the back of queue. pop() -- Removes the element from in front of queue. peek() -- Get the front element. empty() -- Return whether the queue is empty. Example:

MyQueue queue = new MyQueue();

queue.push(1); queue.push(2);
queue.peek(); // returns 1 queue.pop(); // returns 1 queue.empty(); // returns false Notes:

You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid. Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack. You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

class MyQueue(object):

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

    def push(self, x):
        """
        Push element x to the back of queue.
        :type x: int
        :rtype: void
        """
        self.queue.append(x)
        

    def pop(self):
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """
        x=self.queue[0]
        del self.queue[0]
        return x
        

    def peek(self):
        """
        Get the front element.
        :rtype: int
        """
        return self.queue[0]
        

    def empty(self):
        """
        Returns whether the queue is empty.
        :rtype: bool
        """
        return self.queue==[]