my code with python. i dont know it fail in test case 7 how to debug def roadsAndLibraries(n, c_lib, c_road, cities): if c_road > c_lib: return c_lib * n

list_cities = set(range(1, n + 1))
visited_cities = set()
city_groups = []

for city_pair in cities:
    set_cities = set(city_pair)
    visited_cities.update(set_cities)
    merged = False

    for i, group in enumerate(city_groups):
        if group & set_cities:
            city_groups[i] = group | set_cities
            merged = True
            break

    if not merged:
        city_groups.append(set_cities)

total_cost = 0

for group in city_groups:
    total_cost += (len(group) - 1) * c_road + c_lib

unvisited_cities = list_cities.difference(visited_cities)
total_cost += len(unvisited_cities) * c_lib

return total_cost