TrimaBinarySearchTree

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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.
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/**
 * 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 == NULL) {
			return NULL;
		}
		TreeNode *new_root = NULL;
	
			if (root->val >= L && root->val <= R) {
				new_root = root;
				new_root->left = trimBST(root->left, L, R);
				new_root->right = trimBST(root->right, L, R);
				
			}
			else if(root->val<L) {
				new_root = trimBST(root->right,L,R);
			}
			else if (root->val > R) {
				new_root = trimBST(root->left, L, R);
			}
		
		return new_root;
	}
};