Perfect shuffle: Difference between revisions

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=={{header|FreeBASIC}}==

<lang freebasic>function is_in_order( d() as uinteger ) as boolean

'tests if a deck is in order

for i as uinteger = lbound(d) to ubound(d)-1

if d(i) > d(i+1) then return false

next i

return true

end function

sub init_deck( d() as uinteger )

for i as uinteger = 1 to ubound(d)

d(i) = i

next i

return

end sub

sub shuffle( d() as uinteger )

'does a faro shuffle of the deck

dim as integer n = ubound(d), i

dim as integer b( 1 to n )

for i = 1 to n/2

b(2*i-1) = d(i)

b(2*i) = d(n/2+i)

next i

for i = 1 to n

d(i) = b(i)

next i

return

end sub

function shufs_needed( size as integer ) as uinteger

dim as uinteger d(1 to size), s = 0

init_deck(d())

do

shuffle(d())

s+=1

if is_in_order(d()) then exit do

loop

return s

end function

dim as uinteger tests(1 to 7) = {8, 24, 52, 100, 1020, 1024, 10000}, i

for i = 1 to 7

print tests(i);" cards require "; shufs_needed(tests(i)); " shuffles."

next i</lang>

{{out}}<pre>

8 cards require 3 shuffles.

24 cards require 11 shuffles.

52 cards require 8 shuffles.

100 cards require 30 shuffles.

1020 cards require 1018 shuffles.

1024 cards require 10 shuffles.

10000 cards require 300 shuffles.