Day22 q2: Sum of Left Leaves #464

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

A leaf is a node with no children.
A left leaf is a leaf that is the left child of another node.

Example 1

image

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

problem link:

https://leetcode.com/problems/sum-of-left-leaves/