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

s

[LeetCode] Trim a Binary Search Tree 修剪一棵二叉樹