Stack Using Queue
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.
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. You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).
Solution
class Stack(object):
def __init__(self):
"""
initialize your data structure here.
"""
self._queue = collections.deque()
def push(self, x):
"""
:type x: int
:rtype: nothing
"""
q = self._queue
q.append(x)
for _ in range(len(q) - 1):
q.append(q.popleft())
def pop(self):
"""
:rtype: nothing
"""
return self._queue.popleft()
def top(self):
"""
:rtype: int
"""
return self._queue[0]
def empty(self):
"""
:rtype: bool
"""
return not len(self._queue)