C# solution using BFS

  • 0

    use flag to indicate it is left or right, then it will be really easy to use BFS to solve this answer

        public int SumOfLeftLeaves(TreeNode root)
            return Helper(root, false);
        private int Helper(TreeNode root, bool isleft)
            if (root == null) return 0;
            // if it is left child
            if(isleft && root.left == null && root.right == null)
                return root.val;
            return Helper(root.left, true) + Helper(root.right, false);

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