I worked on the easy part:
pfr =. ((] (<"1@[ { ])~ ((0 1&(|."_1)&.|:@[)`(-"1 |.)@.(+./@]) =/) @
($@] #: (i.~ ,))) ];.0)~
; _2 pf&pfr\ 'allisdiscoveredfleex'
pmqfabhwewzddrrgtrbz
; _2 (];.0 pf)&pfr\ 'pmqfabhwewzddrrgtrbz'
allisdiscoveredfleex
I can now add monad u;.0 to my Life List.
(you would also need a preconditioner to handle double letters and
odd-length input).
I was hoping the same program would work for the hard part, but I wasn't
sure what to do when the two letters match in more than one axis.
Henry Rich
On 2/19/2011 7:40 AM, Kip Murray wrote:
> The Playfair cipher http://en.wikipedia.org/wiki/Playfair_cipher is based on
> a 5
> by 5 character array that treats i and j as equivalent:
>
> paswo
> rdbce
> fghik
> lmnqt
> uvxyz
>
> To encode “All is discovered flee” you replace pairs of letters
> al li sd is co ve re df le ex with pairs diagonally opposite, one to the
> right,
> or one below (wrapping) from the table, getting
>
> pm qf ab hw ew zd dr rg tr bz
>
> Your mission, should you decide to accept it, is to write j code for
> enciphering
> and deciphering, given the five by five table. That’s the easy part. The
> hard
> part is to design and implement an analogous cipher that uses the 3 by 3 by 3
> character array below to replace triples of letters alx _is _di sco ver ed_
> fle ex_
>
> pas
> wor
> dbc
>
> efg
> hij
> klm
>
> nqt
> uvx
> yz_
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
