Class LongestCommonSubsequence
 All Implemented Interfaces:
SimilarityScore<Integer>
The Longest common subsequence algorithm returns the length of the longest subsequence that two strings have in
common. Two strings that are entirely different, return a value of 0, and two strings that return a value
of the commonly shared length implies that the strings are completely the same in value and position.
Note. Generally this algorithm is fairly inefficient, as for length m, n of the input
CharSequence
's left
and right
respectively, the runtime of the
algorithm is O(m*n).
As of version 1.10, a more spaceefficient of the algorithm is implemented. The new algorithm has linear space complexity instead of quadratic. However, time complexity is still quadratic in the size of input strings.
The implementation is based on Hirschberg's Longest Commons Substring algorithm (cited below).
For further reading see:
 Lothaire, M. Applied combinatorics on words. New York: Cambridge U Press, 2005. 1213
 D. S. Hirschberg, "A linear space algorithm for computing maximal common subsequences," CACM, 1975, pp. 341343.
 Since:
 1.0

Constructor Summary

Method Summary
Modifier and TypeMethodDescriptionapply
(CharSequence left, CharSequence right) Calculates the longest common subsequence similarity score of twoCharSequence
's passed as input.logestCommonSubsequence
(CharSequence left, CharSequence right) Deprecated.Deprecated as of 1.2 due to a typo in the method name.longestCommonSubsequence
(CharSequence left, CharSequence right) Computes the longest common subsequence between the twoCharSequence
's passed as input.int[][]
longestCommonSubstringLengthArray
(CharSequence left, CharSequence right) Deprecated.Deprecated as of 1.10.

Constructor Details

LongestCommonSubsequence
public LongestCommonSubsequence()


Method Details

apply
Calculates the longest common subsequence similarity score of twoCharSequence
's passed as input.This method implements a more efficient version of LCS algorithm which has quadratic time and linear space complexity.
This method is based on newly implemented
algorithmB(CharSequence, CharSequence)
. An evaluation using JMH revealed that this method is almost two times faster than its previous version. Specified by:
apply
in interfaceSimilarityScore<Integer>
 Parameters:
left
 first character sequenceright
 second character sequence Returns:
 length of the longest common subsequence of
left
andright
 Throws:
IllegalArgumentException
 if either String inputnull

logestCommonSubsequence
Deprecated.Deprecated as of 1.2 due to a typo in the method name. UselongestCommonSubsequence(CharSequence, CharSequence)
instead. This method will be removed in 2.0.Computes the longest common subsequence between the twoCharSequence
's passed as input.Note, a substring and subsequence are not necessarily the same thing. Indeed,
abcxyzqrs
andxyzghfm
have both the same common substring and subsequence, namelyxyz
. However,axbyczqrs
andabcxyzqtv
have the longest common subsequencexyzq
because a subsequence need not have adjacent characters.For reference, we give the definition of a subsequence for the reader: a subsequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements.
 Parameters:
left
 first character sequenceright
 second character sequence Returns:
 the longest common subsequence found
 Throws:
IllegalArgumentException
 if either String inputnull

longestCommonSubsequence
Computes the longest common subsequence between the twoCharSequence
's passed as input.This method implements a more efficient version of LCS algorithm which although has quadratic time, it has linear space complexity.
Note, a substring and subsequence are not necessarily the same thing. Indeed,
abcxyzqrs
andxyzghfm
have both the same common substring and subsequence, namelyxyz
. However,axbyczqrs
andabcxyzqtv
have the longest common subsequencexyzq
because a subsequence need not have adjacent characters.For reference, we give the definition of a subsequence for the reader: a subsequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements.
 Parameters:
left
 first character sequenceright
 second character sequence Returns:
 the longest common subsequence found
 Throws:
IllegalArgumentException
 if either String inputnull
 Since:
 1.2

longestCommonSubstringLengthArray
Deprecated.Deprecated as of 1.10. A more efficient implementation for calculating LCS is now available. UselongestCommonSubsequence(CharSequence, CharSequence)
instead to directly calculate the LCS. This method will be removed in 2.0.Computes the lcsLengthArray for the sake of doing the actual lcs calculation. This is the dynamic programming portion of the algorithm, and is the reason for the runtime complexity being O(m*n), where m=left.length() and n=right.length(). Parameters:
left
 first character sequenceright
 second character sequence Returns:
 lcsLengthArray
