old_contents: // Time:  O(n)
  // Space: O(h)
  
  /**
   * Definition for a binary tree node.
   * struct TreeNode {
   *     int val;
   *     TreeNode *left;
   *     TreeNode *right;
   *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
   * };
   */
  class Solution {
  public:
      TreeNode* trimBST(TreeNode* root, int L, int R) {
          if (!root) {
              return nullptr;
          }
          if (root->val < L) {
              return trimBST(root->right, L, R);
          }
          if (root->val > R) {
              return trimBST(root->left, L, R);
          }
          root->left = trimBST(root->left, L, R);
          root->right = trimBST(root->right, L, R);
          return root;
      }
  };
  
new_contents: # Time:  O(n)
  # Space: O(h)
  
  # 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
  
  # Definition for a binary tree node.
  # class TreeNode(object):
  #     def __init__(self, x):
  #         self.val = x
  #         self.left = None
  #         self.right = None
  
  class Solution(object):
      def trimBST(self, root, L, R):
          """
          :type root: TreeNode
          :type L: int
          :type R: int
          :rtype: TreeNode
          """
          if not root:
              return None
          if root.val < L:
              return self.trimBST(root.right, L, R)
          if root.val > R:
              return self.trimBST(root.left, L, R)
          root.left, root.right = self.trimBST(root.left, L, R), self.trimBST(root.right, L, R)
          return root
      
  
subject: Update trim-a-binary-search-tree.py