DAY 29
0
Software Development

原始題目

Given the `root` of a binary tree, return the sum of all left leaves.

Example 1:

``````Input: root = [3,9,20,null,null,15,7]
Output: 24
Explanation: There are two left leaves in the binary tree, with values 9 and 15 respectively.
``````

Example 2:

``````Input: root = [1]
Output: 0
``````

Constraints:

• The number of nodes in the tree is in the range `[1, 1000]`.
• `-1000 <= Node.val <= 1000`

題目分析

``````if (node->left != NULL && node->left->left == NULL && node->left->right == NULL) {
找到左子葉
}
``````

解題過程

``````# 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 not root:
return 0

left_left_leaves_sum = self.sumOfLeftLeaves(root.left)
right_left_leaves_sum = self.sumOfLeftLeaves(root.right)

cur_left_leaf_val = 0
if root.left and not root.left.left and not root.left.right:
cur_left_leaf_val = root.left.val

return cur_left_leaf_val + left_left_leaves_sum + right_left_leaves_sum
``````