[6, 6, 3, 6, 6, 6, 6, 6, 6, 6]
{3: {3}, 6: {1, 2, 4, 5, 6, 7, 8, 9, 10}}
Bridging cities 2 (group 6 ) and 3 (group 3 )
Bridging cities 3 (group 3 ) and 4 (group 6 )