LeetCode 257. Binary Tree Paths

'''
Given a binary tree, return all root-to-leaf paths.
Note: A leaf is a node with no children.
'''

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

#20ms, 11MB
class Solution(object):
    def binaryTreePaths(self, root):
        """
        :type root: TreeNode
        :rtype: List[str]
        """
        if not root: return []
        if not root.left and not root.right: return [str(root.val)]
       
        connector = '->'
        self.result = []
       
        def pathstr(root, current):
            if not root:
                pass
            elif not root.left and not root.right:
                current += '->'+str(root.val)
                self.result.append(current[2:])
            else:
                current += '->'+str(root.val)
                pathstr(root.left, current)
                pathstr(root.right, current)
       
        pathstr(root, '')
       
        return self.result