# 深度优先搜索，遍历所有路径
class Solution(object):
def binaryTreePaths(self, root):
"""
:type root: TreeNode
:rtype: List[str]
"""
res = []
if root is None:
return res
def helper(node, pre_path, res):
if node.left is None and node.right is None:
res.append(pre_path + str(node.val))
if node.left:
left_pre_path = pre_path + str(node.val) + "->"
helper(node.left, left_pre_path, res)
if node.right:
right_pre_path = pre_path + str(node.val) + "->"
helper(node.right, right_pre_path, res)
helper(root, "", res)
return res
