trimBST.txt

669. Trim a Binary Search Tree

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.

class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int low, int high) {
            if(!root){
                return root;
            }

            if(root -> val >= low && root -> val <= high){
                root -> left = trimBST(root-> left, low, high);
                root -> right = trimBST(root -> right, low, high);

                return root;
            }

            if(root -> val < low){
                return trimBST(root -> right , low, high);
            }
            else
            return trimBST(root ->left , low, high);
    }
};