NAME
LCS - Longest Common Subsequence
SYNOPSIS
use LCS;
my $lcs = LCS->LCS( [qw(a b)], [qw(a b b)] );
# $lcs now contains an arrayref of matching positions
# same as
$lcs = [
[ 0, 0 ],
[ 1, 2 ]
];
my $all_lcs = LCS->allLCS( [qw(a b)], [qw(a b b)] );
# same as
$all_lcs = [
[
[ 0, 0 ],
[ 1, 1 ]
],
[
[ 0, 0 ],
[ 1, 2 ]
]
];
DESCRIPTION
LCS is an implementation based on the traditional LCS algorithm.
It contains reference implementations working slow but correct.
Also some utility methods are added to reformat the result.
CONSTRUCTOR
new()
Creates a new object which maintains internal storage areas for the
LCS computation. Use one of these per concurrent LCS() call.
METHODS
LCS(\@a,\@b)
Finds a Longest Common Subsequence, taking two arrayrefs as method
arguments. It returns an array reference of corresponding indices,
which are represented by 2-element array refs.
# position 0 1 2
my $a = [qw(a b )];
my $b = [qw(a b b)];
my $lcs = LCS->LCS($a,$b);
# same like
$lcs = [
[ 0, 0 ],
[ 1, 1 ]
];
LLCS(\@a,\@b)
Calculates the length of the Longest Common Subsequence.
my $llcs = LCS->LLCS( [qw(a b)], [qw(a b b)] );
print $llcs,"\n"; # prints 2
# is the same as
$llcs = scalar @{LCS->LCS( [qw(a b)], [qw(a b b)] )};
allLCS(\@a,\@b)
Finds all Longest Common Subsequences. It returns an array reference
of all LCS.
my $all_lcs = LCS->allLCS( [qw(a b)], [qw(a b b)] );
# same as
$all_lcs = [
[
[ 0, 0 ],
[ 1, 1 ]
],
[
[ 0, 0 ],
[ 1, 2 ]
]
];
The purpose is mainly for testing LCS algorithms, as they only return
one of the optimal solutions. If we want to know, that the result is
one of the optimal solutions, we need to test, if the solution is
part of all optimal LCS:
use Test::More;
use Test::Deep;
use LCS;
use LCS::Tiny;
cmp_deeply(
LCS::Tiny->LCS(\@a,\@b),
any(@{LCS->allLCS(\@a,\@b)} ),
"Tiny::LCS $a, $b"
);
lcs2align(\@a,\@b,$LCS)
Returns the two sequences aligned, missing positions are represented
as empty strings.
use Data::Dumper;
use LCS;
print Dumper(
LCS->lcs2align(
[qw(a b)],
[qw(a b b)],
LCS->LCS([qw(a b)],[qw(a b b)])
)
);
# prints
$VAR1 = [
[
'a',
'a'
],
[
'',
'b'
],
[
'b',
'b'
]
];
align(\@a,\@b)
Returns the same as lcs2align() via calling LCS() itself.
sequences2hunks($a, $b)
Transforms two array references of scalars to an array of hunks (two
element arrays).
hunks2sequences($hunks)
Transforms an array of hunks to two arrays of scalars.
use Data::Dumper;
use LCS;
print Dumper(
LCS->hunks2sequences(
LCS->LCS([qw(a b)],[qw(a b b)])
)
);
# prints (reformatted)
$VAR1 = [ 0, 1 ];
$VAR2 = [ 0, 2 ];
align2strings($hunks, $gap_character)
Returns two strings aligned with gap characters. The default gap
character is '_'.
use Data::Dumper;
use LCS;
print Dumper(
LCS->align2strings(
LCS->lcs2align([qw(a b)],[qw(a b b)],LCS->LCS([qw(a b)],[qw(a b b)]))
)
);
$VAR1 = 'a_b';
$VAR2 = 'abb';
fill_strings($string1, $string2, $fill_character)
Returns both strings filling up the shorter with $fill_character to
the same length.
The default $fill_character is '_'.
clcs2lcs($compact_lcs)
Convert compact LCS to LCS.
lcs2clcs($compact_lcs)
Convert LCS to compact LCS.
max($i, $j)
Returns the maximum of two numbers.
EXPORT
None by design.
STABILITY
Until release of version 1.00 the included methods, names of methods
and their interfaces are subject to change.
Beginning with version 1.00 the specification will be stable, i.e. not
changed between major versions.
REFERENCES
Ronald I. Greenberg. Fast and Simple Computation of All Longest Common
Subsequences, http://arxiv.org/pdf/cs/0211001.pdf
Robert A. Wagner and Michael J. Fischer. The string-to-string
correction problem. Journal of the ACM, 21(1):168-173, 1974.
SOURCE REPOSITORY
http://github.com/wollmers/LCS
AUTHOR
Helmut Wollmersdorfer
COPYRIGHT
Copyright 2014- Helmut Wollmersdorfer
LICENSE
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
SEE ALSO