Solutions to the circle hackathon challenge

#.md

There is a 7-digit number with all distinct digits. The product of the first 3 digits = product of the middle 3 digits = product of the last 3 digits. Find the number.

a16z.coffee

fits = (str) ->
  p1 = str.charAt(0) * str.charAt(1) * str.charAt(2)
  p2 = str.charAt(2) * str.charAt(3) * str.charAt(4)
  p3 = str.charAt(4) * str.charAt(5) * str.charAt(6)
  return p1 == p2 && p2 == p3

for x in [1000000..9999999]
  if /^(?:(.)(?!.*?\1))*$/.test(x) && fits("#{x}")
    console.log("#{x}".charAt(3))
    return

a16z.prolog

% Swift's solution to the A16Z Hackathon challenge.

all_distinct([]).
all_distinct([_]).
all_distinct([Head|Tail]) :- not(member(Head, Tail)), all_distinct(Tail).

set_bounds(X) :- between(0,9,X).

has_property([A,B,C,D,E,F,G]) :-
  P1A is A * B, P1 is P1A * C,
  P2A is C * D, P2 is P2A * E,
  P3A is E * F, P3 is P3A * G,
  P1 = P2, P2 = P3.

a16z(List) :-
  length(List, 7),
  all_distinct(List),
  has_property(List),
  !.

solve(Puzzle) :-
  maplist(set_bounds, Puzzle),
  a16z(Puzzle).

Relevant: http://discovercircle.com/hackathon

Yo can you explain the regex on that?

nvm got it!