day03a.dl

.decl report(bits:symbol)
.input report(filename="day03.facts",delimiter=" ")

.decl bitpos(pos:number)
bitpos(pos) :- pos = range(0, 12, 1).

.decl most_common_bit(position:number, most_common:number)
most_common_bit(pos, most_common) :-
  //pos = range(0, 12, 1), // crashes
  bitpos(pos),
  ones = count : { report(bits), substr(bits, 11 - pos, 1) = "1" },
  zeroes = count : { report(bits), substr(bits, 11 - pos, 1) = "0" },
  ( (ones > zeroes, most_common = 1)
  ; (zeroes > ones, most_common = 0)
  ).

.decl gamma_rate(g:number)
gamma_rate(g) :-
  g = sum u : { most_common_bit(pos, b), u = b bshl pos }.

.decl epsilon_rate(e:number)
epsilon_rate(e) :-
  e = sum u : { most_common_bit(pos, b), u = (b lxor 1) bshl pos }.

.decl answer(c:number)
.output answer

answer(g * e) :-
  gamma_rate(g),
  epsilon_rate(e).