Discussion on: Daily Challenge #149 - Fun with Lamps

fun gen_alt (starting, next, len) = List.tabulate(len, fn x => if x mod 2 = 0 then starting else next)

fun diff ([], []) = 0
  | diff (x::xs, y::ys) = (if x = y then 0 else 1) + diff(xs, ys)
  | diff (_, _) = ~1 (* List lengths don't match for some reason *)

fun lamps [] = 0
  | lamps i = Int.min(diff(i, gen_alt(0, 1, length i)), diff(i, gen_alt(1, 0, length i)))