Leetcode: Sum Root to Leaf Numbers @Python

# 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 crtNum(self, crt, num):
        if not crt.left and not crt.right:
            return num*10+crt.val
        elif not crt.left:
            return self.crtNum(crt.right,num*10+crt.val)
        elif not crt.right:
            return self.crtNum(crt.left,num*10+crt.val)
        else:
            return self.crtNum(crt.right,num*10+crt.val)+self.crtNum(crt.left,num*10+crt.val)
        
    def sumNumbers(self, root):
        if root:
            return self.crtNum(root,0)
        else:
            return 0