spoj_COINS.fsx

let computeMaxDollars (n:int) (memo:Dictionary<int64,int64>)= 
   
  let rec computeMaxDollars' (ni:int64) = 
    if ni = 0L || ni = 1L then // base case 
      ni
    else
      match memo|> Memo.tryFind ni with 
      | Some (nx) -> nx  // found in memo. Returning Result. 
      | None     -> 
        let f  = computeMaxDollars' 
        let nx = 
          (ni/2L, ni/3L, ni/4L)
          |> (fun (x,y,z) -> (f x) + (f y) + (f z)) 
          |> (fun nx -> Math.Max(ni,nx))

        memo|> Memo.add ni nx |> ignore // storing the result in memo
        nx
  computeMaxDollars' (n|>int64)