pythagorean-triplet.ml

let triplet target =
  let rec next a b =
    let c = target - a - b in
    match (a * a + b * b == c * c) with
    | true  -> a * b * c
    | false  when b < target / 2 -> next a (b + 1)
    | false  when a < target / 3 -> next (a + 1) (a + 2)
    | _ -> 0 in
  next 1 2

let _ = triplet 1000 (* ==> 31875000 *)