CareerCup

create and array of structure of Months of size 30.
parse the table, according to product & month update corresponding entry

after complete parsing, print the result for all non-zero entries from 1st product to 30th product.

Make sure to keep entry in lexicographic order

use LinkedHashMap<String, int[]> to store data in java.

public static void getProdCount(String[][] input){
        LinkedHashMap<String, int[]> map = new  LinkedHashMap<String, int[]>();
        for(int i=0;i<input.length;i++){
            int[] list= map.get(input[i][0]);
            if(list==null){
                list = new int[12];

            }
            String date = input[i][1];   //2/1/1980
            int index = Integer.parseInt(date.split("/")[0])-1;
            list[index] = list[index]+1;
            map.put(input[i][0],list);
        }

        for(Map.Entry<String, int[]> entry:map.entrySet()){
            int[] list = entry.getValue();
            for(int i=0;i<list.length;i++){
                if(list[i]>0)
                    System.out.println(entry.getKey()+"    "+getMonth(i) +"   "+list[i]);
            }
        }
    }

    public static String getMonth(int i){
        String[] month = {"Jan","Feb","March","April","May","June","July","Aug","Sep","Oct","Nov","Dec"};
        return month[i];
    }

pass input as :
String[][] input = {
{"A","1/1/1980"},
{"B","1/1/1980"},
{"C","1/1/1980"},
{"A","1/1/1980"},
{"B","1/1/1980"},
{"C","2/1/1980"},
{"A","7/1/1980"},
{"B","1/1/1980"},
{"C","5/1/1980"},
{"A","3/1/1980"},
{"B","1/1/1980"},
{"C","2/1/1980"}};

class Program
    {
        static void Main(string[] args)
        {
            List<Sales> x = new List<Sales>();

            x.Add(new Sales{productName="A",date=DateTime.Parse("1/1/1980")});
              x.Add(new Sales{productName="B",date=DateTime.Parse("2/1/1980")});
              x.Add(new Sales{productName="A",date=DateTime.Parse("1/2/1980")});

              x.Add(new Sales{productName="C",date=DateTime.Parse("1/1/1980")});

            var t  = from z in x group z by new {m=z.date.ToString("MMMM"),z.productName} into temp   select new {ProductName =temp.Key.productName ,Month =temp.Key.m,Copies =temp.Count()} ;

            foreach (var x1 in t)
            {
                Console.WriteLine(x1.ProductName+ " "+x1.Month+ " "+x1.Copies);
            }

            }

        public class Sales
        {
            public string productName;
            public DateTime date;
        }
    }