import queue

class BT_Array_BFS:
    def __init__(self, nums):
        self.__nums = nums

    def traverse_levelorder_bfs(self):
        if len(self.__nums) == 0:
            return

        q = queue.Queue()

        # initialzation
        i_root = 0
        q.put(i_root)

        while True:
            if q.qsize() == 0:
                break

            i = q.get()
            if i >= len(self.__nums):
                continue
            if self.__nums[i] == None:
                continue

            print(self.__nums[i], end = " ")

            i_left = (i+1) * 2 - 1
            i_right = (i+1) * 2

            q.put(i_left)
            q.put(i_right)


if __name__ == '__main__':
    nums = [
        5,
        2, 6,
        1, 4, None, 7,
        None, None, 3, None, None, None, None, None]
    bt = BT_Array_BFS(nums)
    print()

    print("\nlevel-order:", end = " ")
    bt.traverse_levelorder_bfs()
    print()