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.
MyQueue queue = new MyQueue(); queue.push(1); queue.push(2); queue.peek(); // returns 1 queue.pop(); // returns 1 queue.empty(); // returns false
- 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.instack = list() self.outstack = list() def push(self, x): """ Push element x to the back of queue. :type x: int :rtype: void """ self.instack.append(x) def pop(self): """ Removes the element from in front of queue and returns that element. :rtype: int """ if len(self.outstack) == 0: self.__pour() return self.outstack.pop() def peek(self): """ Get the front element. :rtype: int """ if len(self.outstack) == 0: self.__pour() return self.outstack[-1] def empty(self): """ Returns whether the queue is empty. :rtype: bool """ return len(self.instack) == 0 and len(self.outstack) == 0 def __pour(self): while len(self.instack) > 0: self.outstack.append(self.instack.pop()) # Your MyQueue object will be instantiated and called as such: # obj = MyQueue() # obj.push(x) # param_2 = obj.pop() # param_3 = obj.peek() # param_4 = obj.empty()