# 0404. Sum of Left Leaves

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

## Description

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

**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`

## ac

```java
```
