Method sumOfLeftLeaves

java/404_Sum_of_Left_Leaves.java:24–40

(TreeNode root)

    } */

    public int sumOfLeftLeaves(TreeNode root) {
        int res = 0;
        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        while (!stack.isEmpty()) {
            TreeNode node = stack.pop();
            if (node != null) {
                if (node.left != null
                    && node.left.left == null
                    && node.left.right == null)
                    res += node.left.val;
                stack.push(node.right);
                stack.push(node.left);
            }
        }
        return res;
    }
}