404. sum of left leaves

 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class  {
    public int sumOfLeftLeaves(TreeNode root) {
        if (root == null) return 0;
      int sum = 0;
        if (root.left != null && root.left.left==null && root.left.right==null) {
            sum += root.left.val;
        }
        sum += sumOfLeftLeaves(root.left);
       sum += sumOfLeftLeaves(root.right);
      return sum;
    }
}