Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

   1
 /   \
2     3
 \
  5

All root-to-leaf paths are:

["1->2->5", "1->3"]

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public IList<string> BinaryTreePaths(TreeNode root) {
        IList<string> paths = new List<string>();
        if (root == null){
            return paths;
        }

        IList<string> leftpaths = BinaryTreePaths(root.left);
        IList<string> rightpaths = BinaryTreePaths(root.right);

        foreach (string p in leftpaths){
            paths.Add (root.val + "->" + p);

        }
        foreach (string p in rightpaths){
            paths.Add (root.val + "->" + p);
        }

        if (paths.Count()==0){

            paths.Add(root.val.ToString());
        }
        return paths;
    }
}