Leet Code 450. Delete Node in a BST

Example 1:

Input: root = [5,3,6,2,4,null,7], key = 3
Output: [5,4,6,2,null,null,7]
Explanation: 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 above BST.

package pep.Day70;

public class LeetCode_450_Delete_Node_in_BST {
    static class TreeNode {
        int val;
        TreeNode left, right;

        TreeNode() {

        }

        TreeNode(int val) {
            this.val = val;
        }

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

    public static TreeNode deleteNode(TreeNode root, int key) {
        if (root == null)
            return null;

        if (root.val < key) {
            // right me jaenge hum
            root.right = deleteNode(root.right, key);
        } else if (root.val > key) {
            // left me jaenge hum
            root.left = deleteNode(root.left, key);
        } else {
            // agr leaf node ko delete krna hoga
            // jab root.left ne null return kiya to jha se yeh
            // call hua hoga ie. iska parent me null add ho jaega aur
            // yeh key wala node delete ho jaega
            if (root.left == null && root.right == null)
                return null;
                // agr woh node delete krni hai jiska sirf ek child hai
            else if (root.left == null || root.right == null)
                return root.left == null ? root.right : root.left;
            else {
                // right wala element uthaya
                TreeNode temp = root.right;
                // right wala element ke left most child pr jaenge
                while (temp.left != null)
                    temp = temp.left;

                // jis root node ko delete krna hai usme leftmost wale ki value daal de
                root.val = temp.val;

                // aab leftmost wale ko delete krne ke lea
                // root node ki right side pr deleteNode call kr denge
                root.right = deleteNode(root.right, root.val);
            }
        }

        return root;
    }
}