Delete a node from 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

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public TreeNode deleteNode(TreeNode root, int val) {
         if (root == null) return root;

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

     public TreeNode findMin(TreeNode n) {
         if (n.left != null) {
             return findMin(n.left);
         }
         return n;
     }
 }