let rec min a =
  let len = Array.length a in
  let index = len - 1 in
  let minimum = a.(index) in

  if a.(index - 1) < minimum then let minimum = a.(index - 1) in minimum else

  if index = 1 then minimum else
    let index = index - 1 in
    min [| a.(index - 1); a.(index)|]
;;