leetcode257. Binary Tree Paths

原题链接https://leetcode.com/problems/binary-tree-paths/
做到这里的时候已经被前面的dfs的题弄到心力憔悴，这题回了口血，啊哈哈哈

Given a binary tree, return all root-to-leaf paths.

Note: A leaf is a node with no children.
Example:

Input:

1
/ \
2 3
\
5

Output: ["1->2->5", "1->3"]

Explanation: All root-to-leaf paths are: 1->2->5, 1->3

class Solution:
    def binaryTreePaths(self, root: TreeNode) -> List[str]:

        def dfs(root, path, res):
            if not root:
                return 
            path = path + "->" + str(root.val)
            if not (root.left or root.right):
                res.append(path[2:])
            dfs(root.left,path,res)
            dfs(root.right,path,res)
        path = ""
        res = []
        dfs(root,path,res)
        return res