二叉树的层平均值

def solve(____):
    from collections import deque
    if not root:
        return []
    result, q = [], deque(____)
    while q:
        total, count = ____, len(____)
        for _ in range(____):
            node = q.popleft()
            total += node.val
            if node.left:
                q.append(____)
            if node.right:
                q.append(____)
        result.append(____)
    return result