Problem Statement

Shuffle the characters of a string in such a way that as many of the character values are in a different position as possible. A shuffle that produces a randomized result among the best choices is to be preferred. A deterministic approach that produces the same sequence every time is acceptable as an alternative. Display the result as follows: The score gives the number of positions whose character value did not change.

Let's start with the solution:

sub best-shuffle(Str $orig) {
    my @s = $orig.comb;
    my @t = @s.pick(*);

    for flat ^@s X ^@s -> \i,\j {
        if i != j and @t[i] ne @s[j] and @t[j] ne @s[i] {
            @t[i,j] = @t[j,i] and last
        }
    }

    my $count = 0;
    for @t.kv -> $k,$v {
        ++$count if $v eq @s[$k]
    }

    @t.join, $count;
}

printf "%s, %s, (%d)\n", $_, best-shuffle $_  for ;