my $pos=0;
foreach my $sbstr ( @$array ) {
       $pos = index $str, $sbstr, $pos;
       substr ($nstring, $pos, length ($sbstr)) = $sbstr;
       $pos++
}   

##</code><code>##

my %after;
foreach my $sbstr ( @$array ) {
       my $pos = index $str, $sbstr, $after{$sbstr}||0;
       substr ($nstring, $pos, length ($sbstr)) = $sbstr;
       $after{$sbstr}=$pos+1;
}