1670.py

from collections import deque


class FrontMiddleBackQueue:
    def __init__(self):
        left = deque()
        right = deque()

    def balance(self):
        if len(self.left) > len(self.right):
            self.right.appendleft(self.left.pop())
        elif len(self.left) + 1 < len(self.right):
            self.left.append(self.right.popleft())

    def pushFront(self, val: int) -> None:
        self.left.appendleft(val)
        self.balance()

    def pushMiddle(self, val: int) -> None:
        if len(self.left) == len(self.right):
            self.right.appendleft(val)
        else:
            self.left.append(val)
        self.balance()

    def pushBack(self, val: int) -> None:
        self.right.append(val)
        self.balance()

    def popFront(self) -> int:
        if not self.right:
            return -1
        val = self.left.popleft() if self.left else self.right.popleft()
        self.balance()
        return val

    def popMiddle(self) -> int:
        if not self.right:
            return -1
        val = (
            self.right.popleft()
            if len(self.left) < len(self.right)
            else self.left.pop()
        )
        self.balance()
        return val

    def popBack(self) -> int:
        if not self.right:
            return -1
        val = self.right.pop()
        self.balance()
        return val


# Your FrontMiddleBackQueue object will be instantiated and called as such:
# obj = FrontMiddleBackQueue()
# obj.pushFront(val)
# obj.pushMiddle(val)
# obj.pushBack(val)
# param_4 = obj.popFront()
# param_5 = obj.popMiddle()
# param_6 = obj.popBack()