【leetcode】404 左叶子之和

https://leetcode.cn/problems/sum-of-left-leaves/description/

【分析】

该题要求左叶子之和。

如果我们对当前节点进行叶子节点的判断，那么我们是不知道当前节点是左叶子还是右叶子的。

所以我们应该在叶子结点的上层（父节点）进行判断。

【代码】

class Solution:
    def sumOfLeftLeaves(self, root) -> int:
        if not root or (root.left is None and root.right is None):
            return 0
        cur = 0
        if root.left and root.left.left is None and root.left.right is None:
            cur = root.left.val
        return cur + self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right)

 【更新代码】

class Solution:
    def sumOfLeftLeaves(self, root) -> int:
        if root is None:
            return 0
        if root.left is None and root.right is None:
            return 0
        if root.left and root.left.left is None and root.left.right is None:
            return self.sumOfLeftLeaves(root.left) + root.left.val + self.sumOfLeftLeaves(root.right)
        return self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right)