二叉树层序遍历

def solve():
    from collections import deque
    class TreeNode:
        def __init__(____):
            self.val = val
            self.left = None
            self.right = None
    root = TreeNode(____)
    root.left = TreeNode(____)
    root.right = TreeNode(____)
    root.left.left = TreeNode(____)
    root.left.right = TreeNode(____)
    result = []
    q = deque(____)
    while q:
        node = q.popleft()
        result.append(str(____))
        if node.left:
            q.append(____)
        if node.right:
            q.append(____)
    print('____'.join(____))