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RE: Was Fun - Each character at most once

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From:
Alistair.McGlinchy
Date:
July 25, 2003 12:17
Subject:
RE: Was Fun - Each character at most once
Message ID:
2F8EDAE44C97B1488728682AC9602FC26CC779@MSHSREXCHGP0001
From: Adam Rice [mailto:adamrice@ntlworld.com] 
> Quoting A. Pagaltzis (pagaltzis@gmx.de):
> > I don't see the problem. You have 36 (or 120) pairs or encoded 
> > characters to allocate, and up to that many input characters. Looks 
> > like just one straightforward mapping.
> 
> The problem is that there are 
> 371993326789901217467999448150835200000000
> possible arrangements of the 36 characters. If most of those 
> work then you'll find one pretty quickly, but if there's only 
> one solution, it'll take something like a million million 
> million million years to find it with a brute force approach. 
> I've thought of some ways of making a brute-force approach a 
> bit smarter and reduce the search space a bit, but I haven't 
> found a quick way of determining if there's a solution or 
> not. For now, the only way to determine that something like
> 
> print"............................."
> 
> is unencodable is to try every possible arrangement of characters.

There's still a few more gotcha's to consider

1) How do you check if the code you are about to test doesn't execute `sudo
rm -R *` or some other malicious code instead of printing your desired
output. 

2) What about the Touring problem? Many of your possible test code will
generate infinite loops (not to mention syntax errors). Touring proved you
can't write a program to check if another program will halt on a given
input.  So you'd need to run all the tests in parallel to ensure you don't
get stuck.

3) Which leads on to another problem. If there is a valid solution will you
find it in time. Suppose the only encoding which is valid turns out to be
something that evals this string;
	sleep 1e1000;print "."x29
	or 
	$n++ while( substr($PI, $n, 10) eq  '1234567890');print "."x29    
	# Anyone know if the decimal expansion of pi has 1234567890 as a
substring yet? 

Given what the aliens in the golf list can do in 36 bytes, I can't imagine
what wonders a brute force algorithm would do ;-)

.... It'll all end in tears I tell you. 

Alistair

PS.  Anyone for a up a UniqPerl@home program :-)


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