$a_i\; \mathrm{xor}\; (last\_ans\mod 10^9)$
by gorokokoro @ 2018-06-06 15:54:15
@[BalanceUhen](/space/show?uid=21121) fixed
by chen_zhe @ 2018-06-06 16:57:50
by ACNOI @ 2018-08-04 08:34:03