new_contents: # Definition for a binary tree node.
  # class TreeNode(object):
  #     def __init__(self, x):
  #         self.val = x
  #         self.left = None
  #         self.right = None
  
  class Solution(object):
      def binaryTreePaths(self, root):
          """
          :type root: TreeNode
          :rtype: List[str]
          """
          if root == None:
              return []
          if root.left == None and root.right == None:
              return [str(root.val)]
          ret = []
          if root.left != None:
              left = self.binaryTreePaths(root.left)
              left = map(lambda x: str(root.val) + '->' + x, left)
              ret += left
          if root.right != None:
              right = self.binaryTreePaths(root.right)
              right = map(lambda x: str(root.val) + '->' + x, right)
              ret += right
          return ret
subject: add binary-tree-paths