import json
from typing import Set

def determine_must_visit_locations(plan_json: dict, db_conn, game_name: str) -> Set[str]:
    # Extract needed Pokemon, find their encounter locations via db, return that set.
    # No route logic here, just data derivation.

    target = None
    for game in plan_json:
        if game["game_name"] == game_name:
            target = game
            break

    if not target:
        return set()
    
    # gather up all the pokemon needed for say crystal and find all the encounter routes/locations
    needed_locations = set()
    
    game_info = db_conn.get_game_id_by_name(game_name)
    
    for key in target["pokemon"]:
        catch_stats = target["pokemon"][key]
        rep = catch_stats["representative"]
        rand = db_conn.get_encounters(rep, "random")
        static = db_conn.get_encounters(rep, "static")
        encounters = []
        encounters.extend(rand)
        encounters.extend(static)

        for encounter in encounters:
            if encounter["game_id"] != game_info["id"]:
                continue
            
            encounter_data = json.loads(encounter["data"])
            needed_locations.add(encounter_data["location"].replace("*", ""))
    return needed_locations