Question

I had an interview question asking this:

text file has following lines>

            1: A C D
            4: A B
            5: D F
            7: A E
            9: B C  

*Every line has a unique integer followed by a colon and one or
more letters. These letters are
delimited spaces (one or more)>

                            #2 Write a short program in the language

of your choice that outputs a sorted
list like

            A: 1 4 7
            B: 4 9
            C: 1 9
            D: 1 5
            E: 7
            F: 5

I’m not looking for someone to solve it, but I always get confused with problems like this. I’d like to do it in C# and was wondering should I store each line in a 2d array? What is the best way to handle this. After storing it how do I relist each line with letters rather then numbers?

Just looking for pointers here.

Answer 1

I will use a Dictionary<string,List<int>> I will read the input and add 1 into the list at keys A,C,D, A at keys A,B etc, so having the result is just a lookup by letter.
So like this, in a non esoteric way:

 string inp = @"1: A C D
            4: A B
            5: D F
            7: A E
            9: B C";
            Dictionary<string, List<int>> res = new Dictionary<string, List<int>>();
            StringReader sr = new StringReader(inp);
            string line;
            while (null != (line = sr.ReadLine()))
            {
                if (!string.IsNullOrEmpty(line))
                {
                    string[] tokens = line.Split(": ".ToArray(),StringSplitOptions.RemoveEmptyEntries);
                    int idx = int.Parse(tokens[0]);
                    for (int i = 1; i < tokens.Length; ++i)
                    {
                        if (!res.ContainsKey(tokens[i]))
                            res[tokens[i]] = new List<int>();
                        res[tokens[i]].Add(int.Parse(tokens[0]));
                    }
                }
            }

res will contain the result of letter->list of numbers.