用两个栈实现队列

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队头插入：每次直接压入左边的栈即可
队尾删除：若右栈不为空，则直接弹出一个值即可；若右栈为空，则将左栈先全部入右栈，再弹出一个数

class CQueue:

    def __init__(self):
        self.left_stack = list()
        self.right_stack = list()


    def appendTail(self, value: int) -> None:
        self.left_stack.append(value)


    def deleteHead(self) -> int:
        if not self.right_stack and not self.left_stack:
            return -1
        if not self.right_stack:
            while self.left_stack:
                self.right_stack.append(self.left_stack.pop())
            return self.right_stack.pop()
        else:
            return self.right_stack.pop()
            



# Your CQueue object will be instantiated and called as such:
# obj = CQueue()
# obj.appendTail(value)
# param_2 = obj.deleteHead()