Anonymous user
Mind boggling card trick: Difference between revisions
→{{header|J}}
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BBBBBB = Black cards in the black pile
True</pre>
=={{header|J}}==
The trick verb returns 0 if the magician's proposition fails, otherwise 1.
<lang J>
NB. A failed assertion looks like this
assert 0
|assertion failure: assert
| assert 0
</lang>
We find that in three runs the trick works.
<lang J>
shuffle =: {~ ?~@:#
f =: (,&.> {:)~
g =: ({.@],(f {:))`((f {.),{:@])@.({.@[)
trick =: 3 :0
DECK =: shuffle 2 | i. 52
'B R' =: shuffle L:_1 > g&.>/(_2 <\ DECK) , < 2 # a:
NB. although I swap the first N cards of each pile,
NB. the piles were shuffled following placement
N =: ? R <.&# B
echo 'prior to swap of ',(":N),' cards'
echo 'black pile ',B{'rB'
echo 'red pile ',R{'rB'
BR =: N {. B
RB =: N {. R
B =: RB , N }. B
R =: BR , N }. R
echo 'after swap'
echo 'black pile ',B{'rB'
echo 'red pile ',R{'rB'
B (-:&(+/) -.) R
)
assert trick''
prior to swap of 10 cards
black pile rBrrrrrBBrrrBrr
red pile BBrBrBBrBBr
after swap
black pile BBrBrBBrBBrrBrr
red pile rBrrrrrBBrr
assert trick''
prior to swap of 6 cards
black pile rBBBBrBBr
red pile rrBBBBrBrBBBBrrBB
after swap
black pile rrBBBBBBr
red pile rBBBBrrBrBBBBrrBB
assert trick''
prior to swap of 3 cards
black pile rBrBrrrBBrr
red pile BrrBrBBrBBBBBBB
after swap
black pile BrrBrrrBBrr
red pile rBrBrBBrBBBBBBB
</lang>
=={{header|Javascript}}==
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