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| from collections import deque
class FrontMiddleBackQueue:
def __init__(self):
self.a = deque()
self.b = deque()
def a2b(self):
if len(self.a) <= len(self.b):
return
self.b.appendleft(self.a.pop())
def b2a(self):
if len(self.b) <= len(self.a) + 1:
return
self.a.append(self.b.popleft())
def pushFront(self, val: int) -> None:
self.a.appendleft(val)
self.a2b()
def pushMiddle(self, val: int) -> None:
self.a.append(val)
self.a2b()
def pushBack(self, val: int) -> None:
self.b.append(val)
self.b2a()
def popFront(self) -> int:
if not self.a and not self.b:
return -1
ans = None
if not self.a:
ans = self.b.popleft()
else:
ans = self.a.popleft()
self.b2a()
return ans
def popMiddle(self) -> int:
if not self.a and not self.b:
return -1
ans = None
if len(self.a) == len(self.b):
ans = self.a.pop()
else:
ans = self.b.popleft()
return ans
def popBack(self) -> int:
if not self.a and not self.b:
return -1
ans = self.b.pop()
self.a2b()
return ans
|