**LeetCode-Inorder Successor in BST

简直想不清楚！！！

iterative： 

TreeNode* inorderSuccessor(TreeNode* root, TreeNode* p) {
    TreeNode* candidate = NULL;
    while (root)
        root = (root->val > p->val) ? (candidate = root)->left : root->right;
    return candidate;
}

recursive：

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

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

predecessor

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

  if (root.val >= p.val) {
    return predecessor(root.left, p);
  } else {
    TreeNode right = predecessor(root.right, p);
    return (right != null) ? right : root;
  }
}