1. # Definition for a binary tree node.
    2. # class TreeNode:
    3. #     def __init__(self, val=0, left=None, right=None):
    4. #         self.val = val
    5. #         self.left = left
    6. #         self.right = right
    7. class Solution:
    8.     result = 0
    9.     def sumOfLeftLeaves(self, root: TreeNode) -> int:
    10.         def helper(root, isleft, result):
    11.             if root == None:
    12.                 return 0
    13.             left = helper(root.left, True, self.result)
    14.             right = helper(root.right, False, self.result)
    15.             depth = max(left, right) + 1
    16.             if depth == 1 and isleft:
    17.                 self.result += root.val
    18.             return depth
    19.         #result = 0
    20.         helper(root, False, self.result)
    22.         return self.result