# [Solved] 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.

## Question

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

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

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 = [1]
Output: 0
```

Constraints:

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

## 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:
if root==None:return 0
stack = [[root,'']]
s = 0

while stack:
curr,kaha_se = stack.pop()
if not curr.left and not curr.right and kaha_se=='l':s+=int(curr.val)
if curr.left: stack.append([curr.left,'l'])
if curr.right: stack.append([curr.right,'r'])

return s```