Comments on: Cedric’s Problem in OCaml

By: Mauricio Fernandez

Mauricio Fernandez — Tue, 08 Jul 2008 15:37:34 +0000

Wheelwright: have you noticed that everybody else is using maxRange =
10000000000 (or 4611686018427387903) as opposed to your maxRange = 32768?

My fastest OCaml implementation uses functional sets represented with two lists
(reminiscent of the classic functional queue).

Here are the times I get on a 3GHz Athlon:

Robert Fischer’s version: 2420ms
pango’s version (no I/O): 569ms
functional sets enc. as two lists: 273ms
functional sets with manual inlining: 217ms

(all versions capped to 10_000_000_000)

You can find the code at http://eigenclass.org/misc/beust.ml and
http://eigenclass.org/misc/beust2.ml.

By: Wheelwright

Wheelwright — Mon, 07 Jul 2008 21:32:05 +0000

Last time I swear, damn it is addictive:

foreach (var n in Enumerable.Range(1, maxRange).Cast())
Response.Write(n.Select(c => c).Distinct().Count() == n.Length ? n : “”);

By: Wheelwright

Wheelwright — Mon, 07 Jul 2008 21:17:24 +0000

Oh forget it, it got mangled because I included html break character

By: Wheelwright

Wheelwright — Mon, 07 Jul 2008 21:15:44 +0000

Sorry, if you want printing this will do the job:

for (int n = 0; n c).Distinct().Count() == n.ToString().Length)
Response.Write(“” + n);

Execution time increased to 00.093 secs

By: Wheelwright

Wheelwright — Mon, 07 Jul 2008 20:11:40 +0000

Enumerable.Range(1, maxRange).Aggregate((total, n) =>
{
var chars = from c in n.ToString() select c;
return total += (chars.Distinct().Count() == chars.Count()) ? n : 0;
}));

With no optimization it calculates all the values from 1 to max-int (maxRange = 32767) in 00.078 seconds on my crusty 512MB 3GHz Pentium 4.

Another (albeit slightly slower) way to do it:

Enumerable.Range(1, maxRange).Select(n =>
{
var chars = from c in n.ToString() select c;
var count = chars.Count();
return chars.Distinct().Count() == count ? n : 0;
}
).Sum())

And if anyone wonders I am using LINQ. Both queries are one-liners, line breaks added for clarity.