using System;

using System.Collections.Generic;           

​

public class Program

{

    static int[] cost;

    static HashSet<int> daySet = new HashSet<int>();

    static int[] memo = new int[366];

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    /*In a country popular for train travel, you have planned some train travelling one year in advance.  The days of the year that you will travel is 

    given as an array days.  Each day is an integer from 1 to 365.

​

    Train tickets are sold in 3 different ways:

​

    a 1-day pass is sold for costs[0] dollars;

    a 7-day pass is sold for costs[1] dollars;

    a 30-day pass is sold for costs[2] dollars.

    The passes allow that many days of consecutive travel.  For example, if we get a 7-day pass on day 2, then we can travel for 7 days: day 2, 3, 4, 5, 6, 7, and 8.*/

    public static int MinCostOfTickets(int[] days, int[] costs)

    {

        cost = costs;

        foreach(var day in days)

        {

            daySet.Add(day);

        }

        return dp(1);

    }

    public static int dp(int i)

    {

        if(i > 365) return 0;

        if(memo[i] != null) return memo[i];

        int ans;

        if (daySet.Contains(i)) {

            ans = Math.Min(dp(i+1) + cost[0],

                               dp(i+7) + cost[1]);

            ans = Math.Min(ans, dp(i+30) + cost[2]);

        } else {

            ans = dp(i+1);

        }

​

        memo[i] = ans;

        return ans;

    }

}