LeetCode 669 Trim a Binary Search Tree

给予树:

    1
   / \
  0   2

  L = 1
  R = 2

输出:
    1
      \
       2

给予树:
    3
   / \
  0   4
   \
    2
   /
  1

  L = 1
  R = 3

输出:
      3
     / 
   2   
  /
 1

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode trimBST(TreeNode root, int L, int R) {
        if (root == null) {
            return root;
        }
        root.left = trimBST(root.left, L, R);
        root.right = trimBST(root.right, L, R);
        if (root.val <= R && root.val >= L) return root;
        if (root.val < L) {
            return root.right;
        } else {
            return root.left;
        }
    }
}