ylee

        private static void CashBack(int total, int minItem, int cashback, int[] pricelist)
        {
            Array.Sort(pricelist);

            Func<int, int, int, int[], int> bill = delegate (int n, int m, int c, int[] list)
             {
                 int sum = 0;
                 for (int i = 0; i < n; i++)
                 {
                     sum += list[i];
                 }

                 if (n >= 5) sum -= 10;
                 if (n >= m) sum -= (n / m) * c;

                 return sum;
             };

            int curBill = 0, max = -1,left =total;

            for (int i = 0; i < pricelist.Length; i++)
            {
                curBill = bill(i, minItem, cashback, pricelist);
                if(curBill < total )
                {
                    left = total - curBill;
                    max = i;
                }
            }
            Console.WriteLine(left+" "+max);

            return;
        }