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#!/usr/bin/perl
use warnings;
use strict;
# Count the subsequences.
sub unique_subsequence {
my ($string, $subsequence) = @_;
if (1 == length $subsequence) {
my $count = () = $string =~ /\Q$subsequence/g;
return $count
}
my $char = substr $subsequence, 0, 1, "";
my ($count, $pos) = (0, 0);
$count += unique_subsequence(substr($string, $pos++), $subsequence)
while -1 != ($pos = index $string, $char, $pos);
return $count
}
# Return all the possible positions that match the subsequence.
sub show_unique_subsequence {
my ($string, $subsequence) = @_;
my @solutions;
for my $sub_pos (0 .. length($subsequence) - 1) {
my $sub_char = substr $subsequence, $sub_pos, 1;
my $str_pos = 0;
my @partial;
push @partial, $str_pos++
while -1 != ($str_pos = index $string, $sub_char, $str_pos);
@solutions = map {
my $solution = $_;
map { $_ > $solution->[-1] ? [@$solution, $_] : () } @partial;
} @solutions;
@solutions = map [$_], @partial unless @solutions; # First character.
}
return \@solutions
}
use Test::More tests => 6;
is unique_subsequence('littleit', 'lit'), 5, 'Example 1';
is unique_subsequence('london', 'lon'), 3, 'Example 2';
is unique_subsequence('london', 'par'), 0, 'Zero';
is_deeply show_unique_subsequence('littleit', 'lit'),
[[0, 1, 2], [0, 1, 3], [0, 1, 7], [0, 6, 7], [4, 6, 7]],
'Show Example 1';
is_deeply show_unique_subsequence('london', 'lon'),
[[0, 1, 2], [0, 1, 5], [0, 4, 5]],
'Show Example 2';
is_deeply show_unique_subsequence('london', 'par'), [], 'Show Zero';
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