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Re^2: Permuting with duplicates and no memory

by jettero (Monsignor)
on Apr 01, 2007 at 15:01 UTC ( #607704=note: print w/ replies, xml ) Need Help??


in reply to Re: Permuting with duplicates and no memory
in thread Permuting with duplicates and no memory

I borrowed this for something and noticed that if $num=8 this produces only 40319 permutations... I made the following el cheapo minor modification on mine.

sub make_orderings { my $num = shift; my @arr = (1 .. $num); my $first = 1; return sub { if( $first ) { $first = 0; return @arr; } my $last = $#arr; my $i = $last - 1; $i-- while 0 <= $i && $arr[$i] >= $arr[$i+1]; return if $i == -1; @arr[$i+1..$last] = reverse @arr[$i+1..$last] if $arr[$i+1] > $arr[$last]; my $j=$i+1; $j++ while $arr[$i] >= $arr[$j]; @arr[$i,$j] = @arr[$j,$i]; return @arr; } }

-Paul


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Re^3: Permuting with duplicates and no memory (off by 1)
by tye (Cardinal) on Apr 02, 2007 at 03:11 UTC

    Just FYI, perhaps you missed this bit from the root node:

    do { print "@ARGV\n"; } while( nextPermut­e(@ARGV) );

    which is also why I called my routine "nextPermute".

    Also note that dragonchild's and my iterators can be reused. For yours to be reusable you probably want to change:

    return if $i == -1;

    to

    if( $i == -1 ) { $first= 1; return; }

    - tye        

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