Design Front Middle Back Queue LeetCode solution in Python

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# Runtime: 176 ms (Top 11.57%) | Memory: 14.6 MB (Top 46.27%)
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class FrontMiddleBackQueue:
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    def __init__(self):
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        self.front = deque()
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        self.back = deque()
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    def _correct_size(self):
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        while len(self.back) > len(self.front):
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            self.front.append(self.back.popleft())
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        while len(self.front) > len(self.back) + 1:
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            self.back.appendleft(self.front.pop())
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    def pushFront(self, val: int) -> None:
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        self.front.appendleft(val)
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        self._correct_size()
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    def pushMiddle(self, val: int) -> None:
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        if len(self.front) > len(self.back):
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            self.back.appendleft(self.front.pop())
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        self.front.append(val)
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        self._correct_size()
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    def pushBack(self, val: int) -> None:
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        self.back.append(val)
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        self._correct_size()
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    def popFront(self) -> int:
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        front = self.front if self.front else self.back
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        ret = front.popleft() if front else -1
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        self._correct_size()
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        return ret
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    def popMiddle(self) -> int:
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        ret = self.front.pop() if self.front else -1
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        self._correct_size()
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        return ret
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    def popBack(self) -> int:
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        back = self.back if self.back else self.front
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        ret = back.pop() if back else -1
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        self._correct_size()
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        return ret