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


# 思考誤區:當只有根節點時，這個根是不能同時作為子節點的，當時在這一點上，思考不過來

class Solution(object):
    def sumOfLeftLeaves(self, root):
        """
        :type root: TreeNode
 
        :rtype: int
        """

        if not root:
            return 0

        if root.left and  not root.left.left and not root.left.right:

            return  root.left.val + self.sumOfLeftLeaves(root.right)


        return self.sumOfLeftLeaves(root.left)+self.sumOfLeftLeaves(root.right)

遞歸與二叉樹_leetcode404