FindCityInfluencedTiles.cs

  //Find each cities area of influence that flood fills out from each city to a max distance based on the city pop
  public Dictionary<HexCell, HexCity> FindCityInfluencedTiles(List<HexCity> cities) {
    var frontier = new List<HexCell>();
    var costSoFar = new Dictionary<HexCell, int>();
    var seed = new Dictionary<HexCell, HexCity>();

    //Set the distance to 0 at all start poitns and each start point its own seed
    foreach(var city in cities){
      frontier.Add(city.Cell);
      costSoFar[city.Cell] = 0;
      seed[city.Cell] = city;
    }

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

      for (HexDirection d = HexDirection.NE; d <= HexDirection.NW; d++) {
        HexCell next = current.GetNeighbor(d);
        if(!costSoFar.ContainsKey(next) && costSoFar[current] < maxDistance){
          costSoFar[next] = costSoFar[current] + 1;
          seed[next] = seed[current];
          frontier.Add(next);
        }
      }
    }

    return seed;
  }
  
  void UpdateCityInfluencedTiles(){

    var cityInfluencedTiles = grid.FindCityInfluencedTiles(cityList);
    var grouped = cityInfluencedTiles.GroupBy(x => x.Value);
    foreach(var groupKey in grouped){
      groupKey.Key.influencedCells = groupKey.Select(x => x.Key).ToList();
    }
  }