[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.

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

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