> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/trees/delete-node-in-a-bst.md).

# Delete Node in a BST

Given a root node reference of a BST and a key, delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST.

Basically, the deletion can be divided into two stages:

1. Search for a node to remove.
2. If the node is found, delete the node.

**Note:** Time complexity should be O(height of tree).

**Example:**

```
root = [5,3,6,2,4,null,7]
key = 3

    5
   / \
  3   6
 / \   \
2   4   7

Given key to delete is 3. So we find the node with value 3 and delete it.

One valid answer is [5,4,6,2,null,null,7], shown in the following BST.

    5
   / \
  4   6
 /     \
2       7

Another valid answer is [5,2,6,null,4,null,7].

    5
   / \
  2   6
   \   \
    4   7
```

```java
class Solution {
    public TreeNode deleteNode(TreeNode root, int key) {
        if (root == null)
            return null;

        if (root.val > key)
            root.left = deleteNode(root.left, key);
        else if (root.val < key)
            root.right = deleteNode(root.right, key);
        else {
            if (root.left == null)
                return root.right;
            if (root.right == null)
                return root.left;

            TreeNode rightSmallest = root.right;
            while (rightSmallest.left != null)
                rightSmallest = rightSmallest.left;
            rightSmallest.left = root.left;
            return root.right;
        }
        return root;
    }
}
```