Playfair cipher: Difference between revisions
→{{header|J}}: Fix to match task specs
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=={{header|J}}==
Rather than implement two versions of the rules, one for encrypt, one for decrypt, let's just make a lookup table (mapping character pairs to character pairs). To decrypt we can look up in the other direction.
'''Implementation:'''
sel=. 'Q' e. y▼
▲<lang J>choose=:3 :0
alph=: (sel { 'JQ') -.~ a. {~ 65 + i.26▼
▲ sel=. 'Q'e.y
norm=: [: dedouble alph restrict ('I' I.@:=&'J'@]} ])`(-.&'Q')@.sel@toupper▼
▲ alph=:(sel{'JQ')-.~a.{~65+i.26
▲ norm=: alph restrict('I' I.@:=&'J'@]} ])`(-.&'Q')@.sel@toupper
''
)
restrict=: ] -. -.~
dedouble=: verb define
while. +./ msk=. =/"1 ] _2 ]\ y do.
y =. (1 2 p. I. msk) ({. , 'X' , }.) y
end.
y
)
choose 'Q'
setkey=:
key=. ~.norm y,alph
ref=: ,/ 2{."1 ~."1 (,"0/~ alph) ,"1 norm 'XQV'
mode=. #. =/"2 inds=. 5 5#:key i. ref
inds0=. (0 3,:2 1)&{@,"2 inds
inds1=. 5|1 0 +"1 inds NB. same column
inds2=. 5|0 1 +"1 inds NB. same row
alt=: key {~ 5 #. mode {"_1 inds0 ,"2 3 inds1 ,:"2 inds2
i. 0 0
)
pairs=:
2{."1 -.&' '"1 ~."1 (_2]\ norm y) ,"1 'XQV'
)
encrypt=:
)
decrypt=:
)</lang>
'''Example use:'''
<lang J> choose 'IJ'
setkey 'playfair example'
encrypt 'Hide the gold in the tree stump'
BM OD ZB XD NA BE KU DM UI XM MO UV IF
decrypt '
HI DE TH EG OL DI NT HE TR EX ES TU MP</lang>
=={{header|Java}}==
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