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