【leetcode】404. 左叶子之和 （python）DFS + BFS

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sumOfLeftLeaves(self, root: Optional[TreeNode]) -> int:
		#方法一：dfs
        isLeafNode = lambda node : not node.left and not node.right

        def dfs(node):
            ans = 0
            if not node:
                return 0
            if node.left:
                ans += node.left.val if isLeafNode(node.left) else dfs(node.left)
            if node.right and not isLeafNode(node.right):
                ans += dfs(node.right)
            return ans
        
        return dfs(root) if root else 0

class Solution:
    def sumOfLeftLeaves(self, root: Optional[TreeNode]) -> int:
        # 方法二：BFS，队列
        isLeafNode = lambda node: not node.left and not node.right

        if not root:
            return 0
        que = [root]
        ans = 0
        while que:
            node = que.pop(0)
            if node.left:
                if isLeafNode(node.left):
                    ans += node.left.val
                else:
                    que.append(node.left)
            if node.right and not isLeafNode(node.right):
                que.append(node.right)
        return ans