$other = "x!4Y";
  $password = $PATTERN; # $PATTERN is aHINTbcd
  $password =~ s/a/x/; # or $password =~ s/a/substr($other,0,1)/e;
  $password =~ s/b/!/;
  $password =~ s/c/4/;
  $password =~ s/d/Y/;

##</code><code>##

  $other = "x!4Y";
  $password = $PATTERN; # $PATTERN is aHINTbcd
  $password =~ tr/abcd/$other/;

##</code><code>##

  $password = substr($other, 0, 1).$HINT.substr($other, 1, 3);

##</code><code>##

  $password = join('', substr($other, 0, 1), $HINT, substr($other, 1, 3));