As Dan Bron indicated, if you are looking for pandigital primes it's best to avoid generating all permutations. Many of the permutations (e.g. ones where the last digit is even) are not prime; generating them only to reject them represents a large wasted effort.
----- Original Message ----- From: David Vaughan <[email protected]> Date: Friday, July 8, 2011 6:03 Subject: Re: [Jprogramming] Checking permutations To: Programming forum <[email protected]> > Yeah, it is for PE - ive done the other pandigital problems in > C, but i wanted to try this one in J. > My biggest problem seems to be trying to flatten the > pandigitals. E.g. > > 9 8 7 6 5 4 3 2 1 > > I need to turn into 987654321. Is it possible to do that or do I > need to do > 1+2*10+3*100+...+9*100000000? > > ___________________________ > > David Vaughan > > On 8 Jul 2011, at 12:38, Ric Sherlock <[email protected]> wrote: > > > Project Euler? > > > > To get the permutations in reverse order you could reverse the > string> or reverse the list of permutation indicies. i.e. > > 0 1 2 3 A. 'cba' > > 3 2 1 0 A. 'abc' > > > > In J you are better off testing the whole array of > permutations rather > > than looping through them, so > > (1&p: # ]) i. 50 > > or > > (#~ 1&p:) i. 50 > > 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 > > > > On Fri, Jul 8, 2011 at 10:53 PM, David Vaughan > > <[email protected]> wrote: > >> I'm trying to find the highest 1-9 pandigital prime, so I > need to get the permutations in reverse order if possible. Also, > how can I apply my primeTest script to the results? > >> > >> primeTest =: 3 : 'if. #@:q:y do. y end. ' > >> This is what I have so far. The rank of y and of the list of > permutations don't match up, and it feels like my 'if.' approach > isnt great. > >> > >> Can anyone offer any advice as to how achieve this? > >> > >> Thanks. > >> > >> ___________________________ > >> > >> David Vaughan > >> > >> On 8 Jul 2011, at 11:29, Ric Sherlock <[email protected]> wrote: > >> > >>> (i.@!@# A. ]) 'abcd' > >>> or > >>> (A.~ i.@!@#) 'abcd' > >>> > >>> see also: > >>> http://rosettacode.org/wiki/Find_the_missing_permutation#J > >>> > >>> On Fri, Jul 8, 2011 at 9:44 PM, David Vaughan > >>> <[email protected]> wrote: > >>>> > >>>> How would you go about getting all the permutations of a > string in J? ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
