LintCode- 二叉树的所有路径

/**
* Definition of TreeNode:
* public class TreeNode {
*     public int val;
*     public TreeNode left, right;
*     public TreeNode(int val) {
*         this.val = val;
*         this.left = this.right = null;
*     }
* }
*/
public class Solution {
/**
* @param root the root of the binary tree
* @return all root-to-leaf paths
*/
public List<String> binaryTreePaths(TreeNode root) {
List<String> result = new ArrayList<String>();
if(root==null) return result;
String str = Integer.toString(root.val);
findPaths(root,str,result);
return result;
}

public void findPaths(TreeNode root, String str,List<String> result){
String left= new String();
String right = new String();
if(root.left!=null)
{
left = str+"->"+Integer.toString(root.left.val);
this.findPaths(root.left,left, result);
}

if(root.right!=null)
{
right = str+"->"+Integer.toString(root.right.val);
this.findPaths(root.right,right,result);
}
if(root.right==null&&root.left==null) result.add(str);
}
}