leetcode 1022 - sum of root-leaf binary num.py

# sum of root to leaf binary numbers | leetcode 1022 | https://leetcode.com/problems/sum-of-root-to-leaf-binary-numbers/
# method: (dfs) for each node, left-shift 1 bit and add val. 
#           return sum of both left and right subtree
#           return sum till now at each leaf

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

class Solution:
    def sumRootToLeaf(self, root) -> int:
        def dfsSum(root, total):
            if root is None:
                return 0
            
            total = (total << 1) | root.val
            
            if root.left is None and root.right is None:
                return total
            
            return dfsSum(root.left, total) + dfsSum(root.right, total)
        
        return dfsSum(root, 0)