In a binary search tree $($BST$),$ the in$-$order successor of a node is the node with the smallest key greater than the key of the given node. Write a recursive function that finds the in$-$order successor of a given node in a BST$.$ You are given the TreeNode structure and must implement the function findSuccessor$($TreeNode root, TreeNode p$)$ where root is the root of the BST and p is the node for which you need to find the successor.

class TreeNode $\{$

int key;

TreeNode left;

TreeNode right;

TreeNode$($int key$)\{$

this.key $=$ key;

left $=$ right $=$ null;

$\}$

$\}$

public TreeNode findSuccessor$($TreeNode root, TreeNode p$)\{$

$//$ Your code

$\}$