binary_trees.py

# 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 sumNumbers(self , root):
        if not root:
            return 0
        return self.sumHelper(root, 0) 
    def sumHelper(self, root, sum):
        if not root:
            return 0
        sum = sum*10 + root.val
        if not root.left and not root.right:
            return sum
        return self.sumHelper(root.left, sum) + self.sumHelper(root.right, sum)