Re: The hardest Euler problem

cac <cac@[EMAIL PROTECTED]
> writes Re: The hardest Euler problem

> Marcel Hendrix wrote:
>> cac <cac@[EMAIL PROTECTED]
> writes Re: The hardest Euler problem

>> Assuming you are doing this in Forth (why else mention it here):

> Actually, no. I was just responding to an ongoing discussion, and
> going off-topic. My bad. My Forth is very rusty; I haven't written
> anything significant in Forth since about '83. However, it is a
> favorite of mine, and I have recently started to work with it again.

> I have been trying some of the problem in Forth, but my brain is
> old and rusty, and it will take time.

If you are solving #191, there can't be much wrong with it.

>> I also find that some of the higher-numbered problems can be
surprisingly
>> simple. Unfortunately, some others can waste a day (44, 45 I can't
solve
>> by brute force).

> I solved 44 quickly by computing lookup tables, and then searching them.
> 45 I solved by brute force.

Anything over 6 seconds is "can't" for me :-) I finally let #44 run, and
it
found the solution in about 4634 seconds. With the below optimization it  
finds the solution in 9.6 seconds.

-- GUESS guesses the generating n for a (possibly) pentagonal number xd.
-- The guess will always be too low and never less than 1. 
-- This is simply (-b+sqrt(b^2-4ac))/2a.
: guess ( xd -- n ) #24 1 M*/ 1. D+ DSQRT 1+  6 /   1- 1 MAX ;

-marcel