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

 public TreeNode trimBST(TreeNode root, int L, int R) {
         if(root == null){
             return null;
         }else if(root.val >= L && root.val <= R){
             root.left = trimBST(root.left, L, R);
             root.right = trimBST(root.right, L, R);
             return root;
         }else if(root.val < L){
             return trimBST(root.right, L, R);
         }else if(root.val > R){
             return trimBST(root.left, L, R);
         }
         return null;
     }

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