[leetcode]Tree-669. 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

class Solution {  
public:  
    TreeNode* trimBST(TreeNode* root, int L, int R) {  
        if (root == nullptr)  
            return 0;  
        if (root->val < L)  
            return trimBST(root->right, L, R);  
        else if (root->val > R)   
            return trimBST(root->left, L, R);  
        else {  
            root->left = trimBST(root->left, L, R);  
            root->right = trimBST(root->right, L, R);  
            return root;  
        }  
    }  
};