Recaman's sequence: Difference between revisions

=={{header|Forth}}==

{{works with|gforth|0.7.3}}

<lang forth>: array ( n -- ) ( i -- addr)

create cells allot

does> swap cells + ;

100 array sequence

: sequence. ( n -- ) cr 0 ?do i sequence @ . loop ;

: ?unused ( n -- t | n )

100 0 ?do

dup i sequence @ = if unloop exit then

loop drop true ;

: sequence-next ( n -- a[n] )

dup 0= if 0 0 sequence ! exit then ( case a[0]=0 )

dup dup 1- sequence @ swap - ( a[n]=a[n-1]-n )

dup dup 0> swap ?unused true = and if

nip exit then drop

dup 1- sequence @ swap + ; ( a[n]=a[n-1]+n )

: sequence-gen ( n -- )

0 ?do i sequence-next i sequence ! loop ;

: sequence-repeated

100 0 ?do

i 0 ?do

i sequence @ j sequence @ = if

cr ." first repeated : a[" i . ." ]=a[" j . ." ]=" i sequence @ . unloop unloop exit then

loop

loop ;

100 sequence-gen

15 sequence.

sequence-repeated</lang>

{{out}}

<pre>0 1 3 6 2 7 13 20 12 21 11 22 10 23 9

first repeated : a[20 ]=a[24 ]=42 ok</pre>