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 DFS
        if root==None:
            return 0
        ans = []
        def dfs(t:TreeNode,b:bool):
            if t==None:
                return 
            dfs(t.left,True)
            if t.left==t.right==None and b==True:
                ans.append(t.val)
            dfs(t.right,False)
        dfs(root,False)
        return sum(ans)