I think this test must be look like:

1
-999 999

or
2
-999 999
1 4

or
2
0 999
1 4

and other with -999 or/ans 999.

P.S.: my bug:
for( long key = how[1998]; key != -1; key = how[key] )
AC:
for( long key = 1998; key != -1; key = how[key] )