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Kotlin-based LeetCode algorithm problem solutions, regularly updated
404\. Sum of Left Leaves
Easy
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:**
![](https://assets.leetcode.com/uploads/2021/04/08/leftsum-tree.jpg)
**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`