题解 | #左叶子之和#

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param root TreeNode类 
# @return int整型
#
class Solution:
    def sumOfLeftLeaves(self , root: TreeNode) -> int:
        # write code here
        if not root:
            return 0
        
        left_node_sum = 0
        if root.left and root.left.left == None and root.left.right == None:
            left_node_sum += root.left.val
        # 我服了这个self.xxx
        left_node_sum += self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right)
        return left_node_sum