*Binary Tree Paths

 1     public List<String> binaryTreePaths(TreeNode root) 
 2     {
 3         List<String> res = new ArrayList<String>();
 4         StringBuilder sb = new StringBuilder();
 5         if(root==null)return res;
 6         helper(root,res,sb);
 7         return res;
 8         
 9     }
10     
11     public void helper(TreeNode root, List<String> res, StringBuilder sb)
12     {
13         if(root.left==null&&root.right==null)
14         {
15             sb.append(root.val);
16             res.add(sb.toString());
17             return ;
18         }
19         
20         sb.append(root.val);
21         sb.append("->");
22         
23         if(root.left!=null)
24         {
25             helper(root.left,res, new StringBuilder(sb)); 
26             
27         }
28         
29         if(root.right!=null)
30         {
31             helper(root.right,res, new StringBuilder(sb));
32         }
33         
34     }