> For the complete documentation index, see [llms.txt](https://jaywin.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jaywin.gitbook.io/leetcode/solutions/0404-sum-of-left-leaves.md).

# 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
```