static TreeNode FixBinaryTree(TreeNode root) 
{
    if (root == null)
        return null;  

    if (root.right != null && 
        Visited.Contains(root.right.val))
        return null;

    Visited.Add(root.val);
    root.right = FixBinaryTree(root.right);
    root.left = FixBinaryTree(root.left);
    return root;
}

public class Solution {
    public int[] FindOriginArray(int[] pref) {
        int[] res = new int[pref.Length];

        // TODO: ваш алгоритм...

        return res;
    }
}

class SeatReserver
{
    SeatReserver(int n) { }
    int Reserve() { }
    void Unreserve(int num) { }
}