LeetCode-404. Sum of Left Leaves

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

Find the sum of all left leaves in a given binary tree.

Example:

    3    
   / \    
  9  20    
    /  \    
   15   7    

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

Solution

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
# recursion
class Solution(object):
    def sumOfLeftLeaves(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        if root.left and not root.left.left and not root.left.right:
            return root.left.val + self.sumOfLeftLeaves(root.right)
        return self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right)

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
# Iterative
class Solution(object):
    def sumOfLeftLeaves(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        s = [root]
        res = 0
        while s:
            node = s.pop()
            if node.left:
                s.append(node.left)
                if not node.left.left and not node.left.right:
                    res += node.left.val
            if node.right:
                s.append(node.right)
        return res