I've been working on a cryptogram solver and discovered this post and found the code useful - I snagged the code for the fisher_yates_shuffle to grab one of my solved cryptograms to recreate one to work on solving and I found that in some instances one or two of the letters in $substit remained the same as it was originally. The line that checks for $i == $j does a next BUT $i keeps on counting down and effectively leaves the unchanged letter alone. I fixed it by incrementing $i before doing the next.

I realize in some cases the shuffle results are okay if this happens, but in a cryptogram, it won't fly... ;-) Just thought I'd throw this info back out there just in case you or anyone else may have a need for the fix.

Here's the modified sub:

## Taken from perlfaq4 (thanks btrott)
sub fisher_yates_shuffle {
  my $array = shift;
  for (my $i = @$array; --$i; ) {    
    my $j = int rand ($i+1);
    # next if $i == $j; # original
    if ($i == $j) {  # this means the letter will be the same as it wa
+s before 
        $i++; # put $i back where it was and get another one
        next; 
    } 
    @$array[$i, $j] = @$array[$j, $i];
  }
  return join '', @$array;
}

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thanks for the original post! I'm learning a little here and there about using perl to solve cryptos... it's gonna take a while, but it's fun!!!