LeetCode 404. Sum of Left Leaves

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题目

Find the sum of all left leaves in a given binary tree.

Example:

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    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

思路

Recursion.

代码

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# 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: TreeNode) -> int:
        if root is None:
            return 0
        res = self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right)
        if root.left and root.left.left is None and root.left.right is None:
            res += root.left.val
        return res