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Here are 2 screenshots of a land mass with 2 different randomly-created regions using the Flood-Fill algorithm.

private void Assign_Hexes_to_Regions ( final Random RNG, List <Integer> frontier_hex_IDs, List <Integer> accompanying_frontier_region_IDs, final Function <Coords, List <Coords>> function_all_adjacent_coords ) { // // use a Flood-Fill technique to assign EACH Hex to EXACTLY ONE Partition // while ( frontier_hex_IDs.size() > 0 ) { // // Randomly select one of the UNASSIGNED Hexes // int random_index = RNG.nextInt( frontier_hex_IDs.size() ); int random_vertex_ID = frontier_hex_IDs.remove( random_index ); int random_region_ID = accompanying_frontier_region_IDs.remove( random_index ); Integer existing_region_ID = this.hex_ID_to_partition_ID.get( random_hex_ID ); if ( existing_region_ID == null ) { // // NO Partition assigned (yet) to this (Random) Hex // this.Assign_Hex_ID_to_Region( random_hex_ID, random_region_ID, frontier_hex_IDs, accompanying_frontier_region_IDs, function_all_adjacent_coords ); } else if ( existing_region_ID != random_region_ID ) { // // This Hex was PREVIOUSLY assigned to a DIFFERENT Region. Thus, // this Hex is at a Region Boundary // this.Get_Region( existing_region_ID ).Add_Boundary_Hex_ID( random_hex_ID ); } } private void Assign_Hex_ID_to_Region ( final int hex_ID, final int region_ID, List <Integer> frontier_hex_IDs, List <Integer> accompanying_frontier_region_IDs, final Function <Coords, List <Coords>> function_all_adjacent_coords ) { // // Assigns the Hex to the specified Region // this.Set_Region_ID_for_Hex_ID( hex_ID, region_ID ); // // Add Adjacent Hexes to the Flood-Fill possibilities // // note: the Get_All_Adjacent_Coords() function determines if the Coordinates Wrap-Around or not // for ( Coords adjacent_vertex_coords : function_all_adjacent_coords.apply( this.space_subset.Get_Space().Get_Coords_from_Vertex_ID( vertex_ID ) ) ) { if ( this.space_subset.Get_Space().Has_Coords( adjacent_vertex_coords ) ) { Integer adjacent_hex_ID = this.space_subset.Get_Space().Get_Hex_ID_from_Coords( adjacent_hex_coords ); if ( this.space_subset.Is_in_Subset( adjacent_hex_ID ) ) { frontier_hex_IDs.add( adjacent_hex_ID ); accompanying_frontier_region_IDs.add( region_ID ); } // // do NOT Add the Adjacent Hex if it is NOT in the Subset // } // // do NOT Add the Adjacent Hex if it is NOT on the Map (incl. Wrap-Around) // } } 

private void Assign_Hexes_to_Regions ( final Random RNG, List <Integer> frontier_hex_IDs, List <Integer> accompanying_frontier_region_IDs, final Function <Coords, List <Coords>> function_all_adjacent_coords ) { // // use a Flood-Fill technique to assign EACH Hex to EXACTLY ONE Region // while ( frontier_hex_IDs.size() > 0 ) { // // Randomly select one of the UNASSIGNED Hexes // int random_index = RNG.nextInt( frontier_hex_IDs.size() ); int random_vertex_ID = frontier_hex_IDs.remove( random_index ); int random_region_ID = accompanying_frontier_region_IDs.remove( random_index ); Integer existing_region_ID = this.hex_ID_to_partition_ID.get( random_hex_ID ); if ( existing_region_ID == null ) { // // NO Region assigned (yet) to this (Random) Hex // this.Assign_Hex_ID_to_Region( random_hex_ID, random_region_ID, frontier_hex_IDs, accompanying_frontier_region_IDs, function_all_adjacent_coords ); } else if ( existing_region_ID != random_region_ID ) { // // This Hex was PREVIOUSLY assigned to a DIFFERENT Region. Thus, // this Hex is at a Region Boundary // this.Get_Region( existing_region_ID ).Add_Boundary_Hex_ID( random_hex_ID ); } } private void Assign_Hex_ID_to_Region ( final int hex_ID, final int region_ID, List <Integer> frontier_hex_IDs, List <Integer> accompanying_frontier_region_IDs, final Function <Coords, List <Coords>> function_all_adjacent_coords ) { // // Assigns the Hex to the specified Region // this.Set_Region_ID_for_Hex_ID( hex_ID, region_ID ); // // Add Adjacent Hexes to the Flood-Fill possibilities // // note: the Get_All_Adjacent_Coords() function determines if the Coordinates Wrap-Around or not // for ( Coords adjacent_vertex_coords : function_all_adjacent_coords.apply( this.space_subset.Get_Space().Get_Coords_from_Vertex_ID( vertex_ID ) ) ) { if ( this.space_subset.Get_Space().Has_Coords( adjacent_vertex_coords ) ) { Integer adjacent_hex_ID = this.space_subset.Get_Space().Get_Hex_ID_from_Coords( adjacent_hex_coords ); if ( this.space_subset.Is_in_Subset( adjacent_hex_ID ) ) { frontier_hex_IDs.add( adjacent_hex_ID ); accompanying_frontier_region_IDs.add( region_ID ); } // // do NOT Add the Adjacent Hex if it is OFF on the Land Mass // } // // do NOT Add the Adjacent Hex if it is NOT on the Map (incl. Wrap-Around) // } }