private List<string> Visit(string sourceUser, string destinationUser, UserVisitedList visited)
{
visited.Visit(sourceUser);
FriendDictionary friendsOfSource = userPathRepository.GetFriendsOf(sourceUser);
if (friendsOfSource.Contains(destinationUser))
{
// we found it.
return new List<string> { sourceUser, destinationUser };
}
// get highest-friendcount friend (that we have not yet visited) and see if that leads to the destination.
// if not, try the Nth friend, until there are no more friends, then give up on this branch.
foreach(TwitterUser friend in friendsOfSource.Friends)
{
if (!visited.Visited(friend.Name))
{
List<string> searchResult = Visit(friend.Name, destinationUser, visited);
if (searchResult != null)
{
// this branch was successful. searchResult already contains friend.Name, so append our name to the head of the list.
searchResult.Insert(0, sourceUser);
return searchResult;
}
}
}
// this branch was not successful, no friends of sourceUser matched destinationUser.
return new List<string>();
}
public IEnumerable<string> FindPath(string sourceUser, string destinationUser)
{
if (sourceUser == destinationUser)
return new List<string> {sourceUser};
var friendsVisited = new UserVisitedList();
return Visit(sourceUser, destinationUser, friendsVisited);
}