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.

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public int sumOfLeftLeaves(TreeNode root) {
         int[] total = new int[];
         helper(root, false, total);
         return total[];
     }

     void helper(TreeNode root, boolean isLeft, int[] total) {
         if (root == null) return;
         if (root.left == null && root.right == null) {
             if (isLeft) {
                 total[] += root.val;
             }
             return;
         } 

         helper(root.left, true, total);
         helper(root.right, false, total);

     }
 }