sub c {
($_,$a)=@_;                                   
map{$h{$_}?$h{$_}:do{$h{$_}=(split//,$a)[$i++]."\0"}}/./g
}

##</code><code>##

sub c {
($_,$a)=@_;$b=$_;  
1 while$b=~s/(.)(.*?)\1/$1$2/g; 
eval"y/$b/$a/";    
$_ 
}

##</code><code>##

sub c {
($_,$a)=@_;$b=$_;  
1 while$b=~s/(.)(.*?)\1/$1$2/g; 
eval"y/\Q$b\E/\Q$a\E/";    
$_ 
}