题目链接

404. 左叶子之和

代码

递归

# 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:
        if root is None:
            return 0 
        if root.left is None and root.right is None:
            return 0
        leftvalue = self.sumOfLeftLeaves(root.left)
        if root.left.left is None and root.left.right is None:
            leftvalue = root.left.val
        rightvalue = self.sumOfLeftLeaves(root.right)

        sum = leftvalue + rightvalue
        return sum

迭代

# 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:
        if root is None:
            return 0 
        st = [root]
        result = 0
        while st:
            node = st.pop()
            if node.left and node.left.left is None and node.left.right is None:
                result += node.left.val
            if node.left:
                st.append(node.left)
            if node.right:
                st.append(node.right)
        return result