Submission #977334

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Source Code Expand

open Complex

let pi2 = 2.0 *. acos(-1.0)

let ( +^ ) = add
let ( -^ ) = sub
let ( *^ ) = mul

let rec fft a =
  let n = Array.length a in
  if n != 1 then
  let ae = Array.init (n/2) (fun i -> a.(2*i)) in
  let ao = Array.init (n/2) (fun i -> a.(2*i+1)) in
    fft ae;
    fft ao;
    let w k = { re = cos(pi2 *. (float k) /. (float n)); im = -. sin(pi2 *. (float k) /. (float n))} in
    for i = 0 to n/2-1 do
      let wi = w i in
        a.(i)     <- ae.(i) +^ wi *^ ao.(i);
        a.(n/2+i) <- ae.(i) -^ wi *^ ao.(i);
    done

let ift a =
  let n = Array.length a in
  for i = 0 to n-1 do
    a.(i) <- conj a.(i)
  done;
  fft a;
  for i = 0 to n-1 do
    a.(i) <- (conj a.(i))
  done

let clp2 x =
  let x = x - 1 in
  let x = x lor (x lsr  1) in
  let x = x lor (x lsr  2) in
  let x = x lor (x lsr  4) in
  let x = x lor (x lsr  8) in
  let x = x lor (x lsr 16) in
  x+1

let n = read_int ()
let rec read_intpairs acc = function
  | 0 -> List.rev acc
  | k -> read_intpairs ((Scanf.scanf " %d %d" (fun x y -> (x, y))) :: acc) (k-1)

let ab = Array.of_list ((0, 0) :: (read_intpairs [] n))

let m = (clp2 (n+1)) lsl 1

let a = Array.init m (fun i -> if i <= n then { re = (float (fst ab.(i))); im = 0.0 } else zero)
let b = Array.init m (fun i -> if i <= n then { re = (float (snd ab.(i))); im = 0.0 } else zero)

let () =
  fft a;
  fft b;
  for i = 0 to m-1 do
    a.(i) <- a.(i) *^ b.(i)
  done;
  ift a;
  for i = 1 to 2*n do
    Printf.printf "%d\n" ((truncate (a.(i).re +. 0.5)) / m)
  done

Submission Info

Judge Result