Trim a Binary Search Tree

Given a binary search tree and the lowest and highest boundaries as L and R, trim the tree so that all its elements lies in [L, R] (R >= L). You might need to change the root of the tree, so the result should return the new root of the trimmed binary search tree.

Example 1:

Input: 
    1
   / 
  0   2

  L = 1
  R = 2

Output: 
    1
      
       2

Example 2:

Input: 
    3
   / 
  0   4
   
    2
   /
  1

  L = 1
  R = 3

Output: 
      3
     / 
   2   
  /
 1

 1 public TreeNode trimBST(TreeNode root, int L, int R) {
 2         if(root == null){
 3             return null;
 4         }else if(root.val >= L && root.val <= R){
 5             root.left = trimBST(root.left, L, R);
 6             root.right = trimBST(root.right, L, R);
 7             return root;
 8         }else if(root.val < L){
 9             return trimBST(root.right, L, R);
10         }else if(root.val > R){
11             return trimBST(root.left, L, R);
12         }
13         return null;
14     }