[lintcode] problem 448 – inorder successor in bst

public class  {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

public TreeNode inorderSuccessor(TreeNode root, TreeNode p) {
    if (root == null)
        return null;

    if (root.val <= p.val)
        return inorderSuccessor(root.right, p);
    else {
        TreeNode node = inorderSuccessor(root.left, p);
        return node == null ? root : node;
    }
}