Sum of Left Leaves

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:

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

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 inorder(self, root, isLeft):
        if root:
            self.inorder(root.left, True)
            if isLeft and not root.left and not root.right:
                self.total += root.val
            self.inorder(root.right, False)

    def sumOfLeftLeaves(self, root: Optional[TreeNode]) -> int:
        self.total = 0
        self.inorder(root, False)
        return self.total