257. Binary Tree Paths

 1      public void appendChildren(TreeNode root,String curPath,List<String> answer) {
 2         if (root == null) return;
 3         if (root.left== null && root.right==null) answer.add(curPath+root.val);
 4         if (root.left!=null) appendChildren(root.left,curPath+root.val+"->",answer);
 5         if (root.right!=null) appendChildren(root.right,curPath+root.val+"->",answer);
 6     }   
 7     
 8     public List<String> binaryTreePaths(TreeNode root) {
 9          if(root == null) return new ArrayList<String>();
10         List<String> result = new ArrayList<>();
11         appendChildren(root,"",result);   
12         return result;
13     }