获取二叉树中所有从根到叶的路径，同时识别方向

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

def binaryTreePaths(root):
    if not root:
        return []
    
    paths = []
    dfs(root, "", paths)
    return paths

def dfs(node, path, paths):
    if not node.left and not node.right:  # 叶子节点
        path += str(node.val)
        paths.append(path)
        return
    
    path += str(node.val) + "->"
    
    if node.left:
        dfs(node.left, path, paths)
    
    if node.right:
        dfs(node.right, path, paths)