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.
Note:
- 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).
Python Solution:
class MyStack(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self._queue = collections.deque()
def push(self, x):
"""
Push element x onto stack.
:type x: int
:rtype: void
"""
self._queue.append(x)
for _ in range(len(self._queue) - 1):
self._queue.append(self._queue.popleft())
def pop(self):
"""
Removes the element on top of the stack and returns that element.
:rtype: int
"""
return self._queue.popleft()
def top(self):
"""
Get the top element.
:rtype: int
"""
return self._queue[0]
def empty(self):
"""
Returns whether the stack is empty.
:rtype: bool
"""
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()
Summary:
- Remember, together with implement queue with stack.
LeetCode: 225. Implement Stack using Queues
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