Rookie3 codesprint - hackerrank - memorization, backtracking and backward processing - pass all test cases

maxScore_studyCode.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MaxScore_studyCode
{
    /// <summary>
    /// Try out the study code
    /// Figure out things to do 
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
            ProcessInput(); 
            //RunTestcase(); 
        }

        public static void ProcessInput()
        {
            int n = Convert.ToInt32(Console.ReadLine());

            string[] data = Console.ReadLine().Split(' ');
            long[] numbers = Array.ConvertAll(data, Int64.Parse);

            long maxScore = GetMaxScore(numbers);
            Console.WriteLine(maxScore);
        }

        public static void RunTestcase()
        {
            var array = new long[] { 4, 8, 5 };
            var result = GetMaxScore(array); 
        }

        public static long GetMaxScore(long[] numbers)
        {
            // Complete this function
            return getMaxScore(new HashSet<long>(numbers), numbers.Sum());
        }

        static Dictionary<long, long> memo = new Dictionary<long, long>();

        /// <summary>
        /// backtracking, memorization, and also doing backward tracking. 
        /// Start from a subsequence with all elements are selected, then choose
        /// last element from any number in the hashset, and then figure out the score. 
        /// </summary>
        /// <param name="sequenceNumbers"></param>
        /// <param name="sum"></param>
        /// <returns></returns>
        public static long getMaxScore(HashSet<long> sequenceNumbers, long sum)
        {
            if (memo.ContainsKey(sum))
            {
                return memo[sum];
            }

            var max = 0L;  // using L stands for long 

            // go over all options for next number to remove 
            // backward tracking, assuming that all numbers are included, 
            // sum is original array's summation. 
            foreach (var number in sequenceNumbers.ToList())
            {
                sequenceNumbers.Remove(number);
                var score = ((sum - number) % number) + getMaxScore(sequenceNumbers, sum - number);

                sequenceNumbers.Add(number);  // back tracking - add number back to the set 
                max = Math.Max(score, max);
            }

            memo[sum] = max;
            return max;
        }
    }
}