Sum of Left Leaves

多加一个状态码表示是从左或是从右过来的就行了

class Solution(object):
    result = 0

    def sumOfLeftLeaves(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        self.helper(root, 0)
        return self.result

    def helper(self, root, status):
        if not root:
            return

        if not root.left and not root.right and status == 1:
            self.result += root.val
            return 

        self.helper(root.left, 1)
        self.helper(root.right, 2)