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LeetCode-Solutions/Python/implement-stack-using-queues.py at master · tehsints/LeetCode-Solutions · GitHub

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# Time: push: O(n), pop: O(1), top: O(1)

# Space: O(n)

import collections

class Queue(object):

def __init__(self):

self.data = collections.deque()

def push(self, x):

self.data.append(x)

def peek(self):

return self.data[0]

def pop(self):

return self.data.popleft()

def size(self):

return len(self.data)

def empty(self):

return len(self.data) == 0

class Stack(object):

# initialize your data structure here.

def __init__(self):

self.q_ = Queue()

# @param x, an integer

# @return nothing

def push(self, x):

self.q_.push(x)

for _ in xrange(self.q_.size() - 1):

self.q_.push(self.q_.pop())

# @return nothing

def pop(self):

self.q_.pop()

# @return an integer

def top(self):

return self.q_.peek()

# @return an boolean

def empty(self):

return self.q_.empty()

# Time: push: O(1), pop: O(n), top: O(1)

# Space: O(n)

class Stack2(object):

# initialize your data structure here.

def __init__(self):

self.q_ = Queue()

self.top_ = None

# @param x, an integer

# @return nothing

def push(self, x):

self.q_.push(x)

self.top_ = x

# @return nothing

def pop(self):

for _ in xrange(self.q_.size() - 1):

self.top_ = self.q_.pop()

self.q_.push(self.top_)

self.q_.pop()

# @return an integer

def top(self):

return self.top_

# @return an boolean

def empty(self):

return self.q_.empty()

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