leetcode——257. 二叉树的所有路径

class Solution:
    def binaryTreePaths(self, root: TreeNode) -> List[str]:
        if not root:
            return []
        res=[]
        def helper(root,temp):
            if not root.left and not root.right:
                res.append(temp+[str(root.val)])
            if root.left:
                helper(root.left,temp+[str(root.val)])
            if root.right:
                helper(root.right,temp+[str(root.val)])
        helper(root,[])
        return [‘->‘.join(a) for a in res]