$ cat 652805.pl
#!/usr/bin/perl -w
#
# Generate all possible subsequences of sequence 1
#
use strict;
use warnings;

# Sequence 1
my @seq_1 = ('a', 'b', 'c', 'd', 'e');

# Count of all possible subsequences
my $s1_max = 2 ** @seq_1;
print "Number of possible subsequences: ", $s1_max,"\n";

# To get each possible subsequence, use a binary number
# as a mask to tell you which digits to print
for my $seq (0 .. $s1_max-1) {
        print "Sequence ", $seq, ": ";
        my $bit = 0;
        while ($bit < @seq_1) {
                print $seq_1[$bit], " " if 2**$bit & $seq;
                ++$bit;
        }
        print "\n";
}
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...roboticus

"Sequence" means that you cannot skip characters in your string.

What you are describing would be a contiguous sequence. Otherwise known as a 'substring'. Skipping characters is permitted, it is their relative positions that makes it a sequence.

Contrast LC subsequence with LC substring.

For the subsequence problem, the characters in the solution must

• appear in both strings. (common)
• appear in the same relative ordering in both strings and the solution. (sequence).
• Be longer than any other set of characters that complies with the above two conditions. (longest)

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

Hrm. I wouldn't call that a sequence, but ok. You problem is still a function of length and nothing more.

It's the sum of 2 ^ (remaining length), from 1 to length. Since we can have any character on or off (essentially).

So you have something length 5, for example. That'd be 1 * 2^0 + 2 * 2 ^1 + 3 * 2^2 + 4 * 2 ^ 3 + 5 * 2 ^4. Just looking at that sequence should give you a good idea of how to right a loop around it.