如何在给定的二叉树中找到最大长度为K的所有根子树？

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def find_max_length_subtrees(root, k):
    result = []
    dfs(root, k, result)
    return result

def dfs(node, k, result):
    if not node:
        return 0
    
    left_length = dfs(node.left, k, result)
    right_length = dfs(node.right, k, result)
    
    subtree_length = left_length + right_length + 1
    
    if subtree_length == k:
        result.append(node)
    
    return subtree_length