# LeetCode 404. Sum of Left Leaves

## Description

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

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 = 
Output: 0
```

Constraints:

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

## Explanation

Traverse and only sum the left leaves.

## Python Solution

``````# 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: TreeNode) -> int:
self.sum_left = 0

self.traverse(root, False)

return self.sum_left

def traverse(self, root, is_left):
if not root:
return

if is_left and not root.left and not root.right:
self.sum_left += root.val

self.traverse(root.left, True)
self.traverse(root.right, False)
``````
• Time Complexity: O(N).
• Space Complexity: O(N).