gistfile1.txt

let fannkuch n =
  begin
  let perm1 = Array.create n 0 in for i = 0 to (n-1) do perm1.[i] <- i done;
  let perm = Array.create n 0
  let count = Array.create n 0
  let mutable flips = 0 
  let mutable maxflips = 0 
  let mutable checksum = 0 
  let mutable nperm = 0
  let mutable r = n
  while r > 0 do 
    for i = 0 to n-1 do perm.[i] <- perm1.[i] done;

    while r <> 1 do count.[r-1] <- r; r <- r - 1; done;

    flips <- 0;
    let k = ref perm.[0] in
    while !k <> 0 do
      let t = ref 0 in
      for i = 0 to !k / 2 do
        t := perm.[i];
        perm.[i] <- perm.[!k - i];
        perm.[!k - i] <- !t;
        done;
        
      k := perm.[0];
      flips <- flips + 1;
      done;

    maxflips <- max maxflips flips;
    if nperm &&& 1 = 0 then checksum <- checksum + flips else checksum <- checksum - flips
    
    let mutable go = true in
    let mutable t = 0 in
    while go do
      if r = n then begin go <- false; r <- 0; end
      else
        begin
        t <- perm1.[0];
        for i = 0 to r - 1 do perm1.[i] <- perm1.[i+1] done;
        perm1.[r] <- t;

        count.[r] <- count.[r] - 1;
        if count.[r] > 0 then go <- false
        else r <- r + 1;
        end
      done;

    nperm <- nperm + 1;
    done;

  (maxflips, checksum);
  end

let _ =
  let n = try int((System.Environment.GetCommandLineArgs()).[1]) with _ -> 7
  let (maxflips, checksum) = fannkuch n
  Printf.printf "%d\nPfannkuchen(%d) = %d\n" checksum n maxflips