题目
Find the sum of all left leaves in a given binary tree.
解题思路
递归，递归的时候传一个标记，是左子树还是右子树
代码
class Solution:
def sumOfLeftLeaves(self, root: TreeNode) -> int:
def sumOfLeft(root, flag):
if not root:
return 0
if flag and not root.left and not root.right:
return root.val
return sumOfLeft(root.left, True) + sumOfLeft(root.right, False)
return sumOfLeft(root, False)
