Leetcode (Python): Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / \
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

Solution:

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

class Solution:
    # @param root, a tree node
    # @return an integer
    
    def sumNumbers(self, root):
        self.sum = 0;
        self.sumNumbersRec(root,0)
        return self.sum
        
    def sumNumbersRec(self, root, partialSum):
        if root == None:
            return
        partialSum = partialSum *10 + root.val;
        if root.left == None and root.right == None:
            self.sum += partialSum
        else:
            self.sumNumbersRec(root.left, partialSum)
            self.sumNumbersRec(root.right, partialSum)