text: /**
   * Definition for a binary tree node.
   * function TreeNode(val) {
   *     this.val = val;
   *     this.left = this.right = null;
   * }
   */
  /**
   * @param {TreeNode} root
   * @param {number} L
   * @param {number} R
   * @return {TreeNode}
   */
  var trimBST = function(root, L, R) {
  	if (!root) return null;
  	if (root.val > R) {
  		return trimBST(root.left, L, R);
  	}
  	if (root.val < L) {
  		return trimBST(root.right, L, R);
  	}
  	root.left = trimBST(root.left, L, R);
  	root.right = trimBST(root.right, L, R);
  	return root;
  };
  