class Solution

{

public:

    int mincostTickets(vector<int>& days, vector<int>& costs)

    {

        unordered_set<int> travel(begin(days), end(days));

        vector<int> dp(days.back()+,);

        for(int i=; i<days.back()+; i++)

        {

            if(travel.find(i) == travel.end())

                dp[i] = dp[i-];

            else

            {

                dp[i] = min(dp[i-]+costs[], dp[max(, i-)]+costs[], dp[max(, i-)]+costs[]);

            }

        }

        return dp[days.back()];

    }

};