ctac.MapService.GetTilesInRadiusGeneric C# (CSharp) Method

        private Dictionary<Vector2, Tile> GetTilesInRadiusGeneric(
            Vector2 center, int distance
            , Func<Vector2, Dictionary<Vector2, Tile>> neighborsFunc
            , Func<Vector2, Vector2, int> distanceFunc
        )
        {
            var ret = new Dictionary<Vector2, Tile>();
            if (distance <= 0) return ret;
            var frontier = new List<Vector2>();

            frontier.Add(center);

            while (frontier.Count > 0)
            {
                var current = frontier[0];
                frontier.RemoveAt(0);

                if (!ret.ContainsKey(current))
                {
                    ret.Add(current, mapModel.tiles[current]);
                }

                var neighbors = neighborsFunc(current);
                foreach (var neighbor in neighbors)
                {
                    //add the neighbor to explore if it's not already being returned
                    //or in the queue or too far away
                    if (
                        !ret.ContainsKey(neighbor.Key)
                        && !frontier.Contains(neighbor.Key)
                        && distanceFunc(neighbor.Key, center) <= distance
                    )
                    {
                        frontier.Add(neighbor.Key);
                    }
                }
            }

            return ret;
        }