Question

I have a List containing a lot of paths. I have a specific path I want to check against this list to see if there are any paths there that uses this path, ie:

f.StartsWith(r.FILENAME) && f != r.FILENAME 

What would be the fastest way of doing this?

edit: Complete function from answer below:

static bool ContainsFragment(string[] paths, string fragment) {     // paths **must** be pre-sorted via Array.Sort(paths);     if (paths.Length == 0) return false;     int index = Array.BinarySearch(paths, fragment);     if (index >= 0 && index+1 < paths.Length)     { //we found it          if (paths[index + 1].StartsWith(fragment) &&             paths[index + 1].EndsWith('.manifest'))         {             return true;         }     }     return false; } 

Answer 1

The fastest way is probably with binary search:

static bool ContainsFragment(string[] paths, string fragment) {     // paths **must** be pre-sorted via Array.Sort(paths);     if (paths.Length == 0) return false;     int index = Array.BinarySearch(paths, fragment);     // we want the index of the *next highest* path     if (index < 0) { // no match         index = ~index;      } else { // exact match         index++; // for strict substring (non-equal)     }     return index < paths.Length && paths[index].StartsWith(fragment); } 

But the cost of sorting the array will outweigh any benefit if you are only doing it a few times; in which case, just scan the array – either with LINQ etc, or just:

bool found = false; for(int i = 0 ; i < paths.Length ; i++) {     if(paths[i].StartsWith(fragment) &&           paths[i].Length != fragment.Length)     {         found = true;         break;     } }