@_ = qw (opt pot top stoop stop pit ipt);
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it will print

opst counted 1 times
oopst counted 1 times
opt counted 3 times
ipt counted 2 times
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Update: you´re right, i misread that. But this does it:

use strict;

my %h;

@_ = qw (opt pot top stoop stop pit ipt);
for ( @_ )
{
    my $last;
    $h{join "", grep 
    { 
        if ( $_ eq $last ) { "" } 
        else               { $last = $_; $_ } 
    } 
    sort split "", $_}++;
}

for ( keys %h )
{
    print "$_ counted $h{$_} times\n";
}
[download]

prints:

opst counted 2 times
opt counted 3 times
ipt counted 2 times
[download]