Question

i’m trying to optimize this code:

   foreach (string id in ids)
   {
     MyClass x = myDictionary[id];
     foreach (var map in Maps)
     {
       if ( x.id == map.SourceId || x.id == map.DestionationId)
       {
           //add id to a hashset
       }
     }
   }

if ids.count is 1600 and Maps.Count is 300 000 in takes around 10 minutes to process.

i’ve tried LINQ, but the results are not a lot better:

   var allIds = Maps.select(map => map.SourceId).Union(Maps.select(map => map.DestinationID)).Distinct();
   var toAdd = from id in Ids
               join mapId in AllIds on id equals mapid
               select id;
  //create hashset based on  toAdd collection.

Can anyone point me to a better solution and if possible explain why linq in this case isn’t much more faster?

Thanks

Answer 1

You have complexity of O(countIds * countMaps), if you put all Maps into 2 dictionaries indexed by source and destination you’ll get O(countIds + countMaps).