class MyStack(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.input_queue = Queue()
self.output_queue = Queue()
def push(self, x):
"""
Push element x onto stack.
:type x: int
:rtype: None
"""
self.input_queue.push(x)
def pop(self):
"""
Removes the element on top of the stack and returns that element.
:rtype: int
"""
size = self.input_queue.size()
if size == 0:
return None
for i in range(size - 1):
self.output_queue.push((self.input_queue.pop()))
item = self.input_queue.pop()
self.input_queue, self.output_queue = self.output_queue, self.input_queue
return item
def top(self):
"""
Get the top element.
:rtype: int
"""
size = self.input_queue.size()
if size == 0:
return None
for i in range(size - 1):
self.output_queue.push((self.input_queue.pop()))
item = self.input_queue.peek()
self.output_queue.push((self.input_queue.pop()))
self.input_queue, self.output_queue = self.output_queue, self.input_queue
return item
def empty(self):
"""
Returns whether the stack is empty.
:rtype: bool
"""
return self.input_queue.is_empty()
def bfs(initial, goal_test, successors):
frontier = Queue()
frontier.push(Node(initial))
explored = {initial}
while not frontier.empty:
node: Node = frontier.pop()
if goal_test(node.state):
return node
for parent in successors(node.state):
if parent in explored:
continue
explored.add(node.state)
frontier.push(Node(parent, node))
return None