# 15. Normal BST to Balanced BST

The problem can be found at the following link: [Question Link](https://practice.geeksforgeeks.org/problems/normal-bst-to-balanced-bst/1)

![](https://badgen.net/badge/Level/Easy/green)

## My Approach

To convert a normal Binary Search Tree (BST) into a balanced BST, I follow these steps:

1. Perform an in-order traversal of the original BST and store the nodes in an array (`arr`) in sorted order.
2. Create a new BST from the sorted `arr` by selecting the middle element as the root node, and then recursively constructing left and right subtrees.
3. Return the new balanced BST.

## Time and Auxiliary Space Complexity

* *Time Complexity*: `O(N)`, where `N` is the number of nodes in the original BST. This is because both the in-order traversal and the creation of the balanced BST are linear operations.
* *Auxiliary Space Complexity*: `O(N)`, where `N` is the number of nodes in the original BST. The auxiliary space is used for the `arr` vector, which stores all the nodes during in-order traversal.

## Code (C++)

```cpp
class Solution {
public:
    vector<int> arr;

    void inorder(Node* node) {
        if (!node)
            return;
        inorder(node->left);
        arr.push_back(node->data);
        inorder(node->right);
    }

    Node* createBST(int low, int high) {
        if (low > high)
            return NULL;

        int mid = (low + high) / 2;
        Node* root = new Node(arr[mid]);

        root->left = createBST(low, mid - 1);
        root->right = createBST(mid + 1, high);

        return root;
    }

    Node* buildBalancedTree(Node* root) {
        inorder(root);
        return createBST(0, arr.size() - 1);
    }
};
```

## Contribution and Support

For discussions, questions, or doubts related to this solution, please visit our [discussion section](https://github.com/getlost01/gfg-potd/discussions). We welcome your input and aim to foster a collaborative learning environment.

If you find this solution helpful, consider supporting us by giving a ⭐ star to the [getlost01/gfg-potd](https://github.com/getlost01/gfg-potd) repository.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://gl01.gitbook.io/gfg-editorials/2023/10-2023-oct-14/15-normal-bst-to-balanced-bst.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.