filter a list of strings in C# -

i'm learning c# reading books , other online tutorials (homeandlearn.co.uk)

i've managed fizzbuzz excercise struggling below excercise. much appreciated.

please explain in detail can learn aswell.

excercise

filter list of strings should pass 6 letter strings composed of 2 concatenated smaller strings in list.

for example, given list

acks, top, cat, gr, by, bar,lap, st, ely, ades

the list should return

stacks, laptop, grades, barely

because these concatenation of 2 other strings:

st + acks = stacks

lap + top = laptop

gr + ades = grades

bar + ely = barely

there lot of ways this. here's 1 uses pairing:

        //grab possible pairings in 1 data structure         list<keyvaluepair<string, string>> pairs = new list<keyvaluepair<string, string>>();         string[] list = { "acks", "top", "cat", "gr", "by", "bar", "lap", "st", "ely", "ades" };         foreach (string first in list)         {             foreach (string second in list)             {                 pairs.add(new keyvaluepair<string, string>(first, second));             }         }          //test each pairing length , whatever else want         list<string> sixletterwords = new list<string>();         foreach (keyvaluepair<string, string> pair in pairs)         {             string testword = pair.key + pair.value;             if (testword.length == 6)             {                 sixletterwords.add(testword);             }         }