CareerCup

//C# Code working for me
//optTaskSeqK("AAABBBCCC", 3);

private static Tuple<string, int> optTaskSeqK(string tasks, int coolTime)
        {
            var taskGp = tasks.GroupBy(s => s).Select(s => new { task = s.Key, count = s.Count() });
            var taskDic = taskGp.ToDictionary(g => g.task, g => g.count);
            var recTaskDic = taskGp.ToDictionary(g => g.task, g => 0);
            var coolTaskDic = taskGp.ToDictionary(g => g.task, g => 0);
            String taskOrder = string.Empty;
            int totalExeTime = 0;
            optTask cuTask = new optTask();
            //int cuTaskExeTime=0;
            for (int seq = 0; seq < tasks.Length; seq++)
            {
                foreach (var key in recTaskDic.Keys)
                {
                    if (coolTaskDic[key] != 0)
                        coolTaskDic[key] -= 1;
                }
                cuTask = getNextOptTask(seq);
                totalExeTime += 1 + coolTaskDic[cuTask.taskCh];
                coolTaskDic[cuTask.taskCh] += coolTime;
                taskOrder += cuTask.taskCh;
            }
            optTask getNextOptTask(int seq)
            {
                var taskGP = taskDic.Where(i => i.Value > 0).GroupBy(i => i.Value).OrderByDescending(i => i.Key).First().ToList();
                //if (taskGp.Count() == 1)
                //    return taskGP.First().Key;              

                var optTask = new optTask { taskCh = '\0', exeTime = int.MaxValue, seq = int.MaxValue };
                var tempTask = new optTask();

                foreach (var ti in taskDic)
                {
                    if (ti.Value > 0)
                    {
                        tempTask = new optTask();
                        tempTask.taskCh = ti.Key;
                        tempTask.count = ti.Value;
                        tempTask.seq = recTaskDic[ti.Key];
                        tempTask.exeTime = 1 + coolTaskDic[ti.Key];
                        optTask = compOptTask(tempTask, optTask);
                    }
                }
                taskDic[optTask.taskCh]--;
                recTaskDic[optTask.taskCh] = seq;
                return optTask;
            };

            optTask compOptTask(optTask t1, optTask t2)
            {
                if (t1.exeTime != t2.exeTime)
                    return t1.exeTime < t2.exeTime ? t1 : t2;
                if (t1.count != t2.count)
                    return t1.count > t2.count ? t1 : t2;
                if (t1.seq != t2.seq)
                    return t1.seq < t2.seq ? t1 : t2;
                return t2;
            }
            return Tuple.Create(taskOrder, totalExeTime);
        }

class optTask
        {
            public char taskCh;
            public int exeTime;
            public int count { get; set; }
            public int seq { get; set; }
        }

Working code

////////////////////////////////////////////////////////////////////////////////////
//Input: "129"
//Output: //ADY,ADZ,AEY,AEZ,AFY,AFZ,BDY,BDZ,BEY,BEZ,BFY,BFZ,CDY,CDZ,CEY,CEZ,CFY,CFZ

//Input: "239"
Output: DGY,DGZ,DHY,DHZ,DIY,DIZ,EGY,EGZ,EHY,EHZ,EIY,EIZ,FGY,FGZ,FHY,FHZ,FIY,FIZ
////////////////////////////////////////////////////////////////////////////////////
var letComb = FindCharProduct("129");
Console.WriteLine($"{string.Join(",", letComb)}");

private static HashSet<string> FindCharProduct(string inDigis)
        {
            var inpDic = new Dictionary<char, List<char>>() {
                { '1',new List<char>() {'A', 'B', 'C'}},
                { '2',new List<char>() { 'D', 'E', 'F' } },
                { '3',new List<char>() { 'G', 'H', 'I' } },
                { '4',new List<char>() { 'J', 'K', 'L' } },
                { '5',new List<char>() { 'M', 'N', 'O' } },
                { '6',new List<char>() { 'P', 'Q', 'R' } },
                { '7',new List<char>() { 'S', 'T', 'U' } },
                { '8',new List<char>() { 'V', 'W', 'X' } },
                { '9',new List<char>() { 'Y', 'Z'} },
            };
            var outDic = new HashSet<string>();            
            digitoLetterComb(inDigis);
            void digitoLetterComb(string strKeys)
            {
                if (!strKeys.Any(char.IsDigit))
                {
                    outDic.Add(strKeys);                    
                    return;
                }
                char digit = strKeys.First(char.IsDigit);
                foreach (var ch in inpDic[digit])
                {
                    digitoLetterComb(strKeys.Replace(digit, ch));
                }
            }
            return outDic;
        }
////////////////////////////////////////////////////////////////////////////////////

This is working for me.

//var repAr = new int[] { 1, 2, 3, 0, 0, 1, 3, 6, 6, 6 };
            var repAr = new int[] { 8, 3, 1, 7, 1, 6, 5, 6, 3 };
            var repList = findRepItemsinFixedRange(repAr);
            Console.WriteLine($"Given Items: {string.Join(",", repAr)}");
            Console.WriteLine($"Repeated Items: {string.Join(",", repList)}");
        

        private static HashSet<int> findRepItemsinFixedRange(int[] repAr)
        {
            var repList = new HashSet<int>();
            for (int indx = 0; indx < repAr.Length; indx++)
            {
                if (repAr[valDecode(repAr[indx])] < repAr.Length)
                    repAr[valDecode(repAr[indx])] = valEncode(repAr[valDecode(repAr[indx])]);
                else
                    repList.Add(valDecode(repAr[indx]));
            }
            for (int indx = 0; indx < repAr.Length; indx++)
                repAr[indx] = valDecode(repAr[indx]);

            return repList;

            int valEncode(int val)
            {
                ////abs encode - WON"T WORK FOR ZERO VALUE
                //return -val;
                return val + repAr.Length;
            }
            int valDecode(int val)
            {
                ////abs decode - WON"T WORK FOR ZERO VALUE
                //return Math.Abs(val);
                if (val >= repAr.Length)
                    return val - repAr.Length;
                return val;
            }
        }