Trim a Binary Search Tree.cpp

/* 

    Solution by Rahul Surana
    
    ***********************************************************


Given the root of a binary search tree and the lowest and highest boundaries as low and high, 
trim the tree so that all its elements lies in [low, high]. 
Trimming the tree should not change the relative structure of the elements that will remain in the tree 
(i.e., any node's descendant should remain a descendant). It can be proven that there is a unique answer.

Return the root of the trimmed binary search tree. Note that the root may change depending on the given bounds.



    ***********************************************************
*/


#include <bits/stdc++.h>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int low, int high) {
        if(root == NULL) return NULL;
        if(root->val < low){
            return trimBST(root->right,low,high);
        }
        if(root->val > high){
            return trimBST(root->left,low,high);
        }
        root->left = trimBST(root->left,low,high);
        root->right = trimBST(root->right,low,high);
        return root;
    }
};