题解 | #左叶子之和#

广度优先遍历，记录当前节点是否为左节点,再判断节点是否为叶子节点

# 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
        queue = [[0, root]]
        res = 0
        while queue:
            f, node = queue.pop(0)
            if not node.left and not node.right and f:
                res += node.val
            if node.left:
                queue.append([1, node.left])
            if node.right:
                queue.append([0, node.right])
        return res