I found your description rather confusing. You are not
interested in substrings, rather in substrings that do not
find repeated characters. (I take it that UCS means Unique
Character Substrings?) For comparison here is another
approach based on recursive splits of the string rather
than repeated calls to index. I have no idea how it
compares for efficiency.
sub tilly_UCS {
my $str = shift;
# Try all cuts. Those that don't fall in 2 are repeats
foreach my $char (split //, $str) {
my @cut = split /\Q$char\E/, $str, -1;
if (2 != @cut) {
my @rejoined = map "$cut[$_-1]$char$cut[$_]", 1..$#cut;
@rejoined = sort {length $b <=> $a} @rejoined;
my @unique = tilly_UCS(shift @rejoined);
foreach my $str (@rejoined) {
if (length($str) < length($unique[0])) {
last; # Avoid useless work, cannot improve
}
my @found = tilly_UCS($str);
if (length($found[0]) > length($unique[0])) {
@unique = @found;
}
elsif (length($found[0]) == length($unique[0])) {
push @unique, @found;
}
}
return @unique;
}
}
# No repeats
return $str;
}
BTW those that don't know what the third argument to
shift did should look it up. You will avoid a commmon
misunderstanding that can lead to bugs.
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