my %adjacency_list = (
                       1 => [2,5,6],
                       2 => [1,3,5,6,7],
                       3 => [2,4,6,7,8],
                       4 => [3,7,8],
                       5 => [1,2,6,9,10],
                       6 => [1,2,3,5,7,9,10,11],
                       7 => [2,3,4,6,8,10,11,12],
                       8 => [3,4,7,11,12],
                       9 => [5,6,10,13,14],
                      10 => [5,6,7,9,11,13,14,15],
                      11 => [6,7,8,10,12,14,15,16],
                      12 => [7,8,11,15,16],
                      13 => [9,10,14],
                      14 => [9,10,11,13,15],
                      15 => [10,11,12,14,16],
                      16 => [11,12,15]
                     );