Sum Root to Leaf Numbers(Python)

SumRootToLeafNumbers.py

"""
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.
"""
# 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):
        if not root:
            return 0
        current=0
        sum=[0]
        self.calSum(root, current, sum)
        return sum[0]
    def calSum(self, root, current, sum):
        if not root:
            return
        current=current*10+root.val
        if not root.left and not root.right:
            sum[0]+=current
            return
        
        self.calSum(root.left, current, sum)
        self.calSum(root.right,current, sum)