info.debatty.java.stringsimilarity

Class LongestCommonSubsequence

java.lang.Object

info.debatty.java.stringsimilarity.LongestCommonSubsequence

All Implemented Interfaces:

StringDistance, Serializable

@Immutable
public class LongestCommonSubsequence
extends Object
implements StringDistance

The longest common subsequence (LCS) problem consists in finding the longest subsequence common to two (or more) sequences. It differs from problems of finding common substrings: unlike substrings, subsequences are not required to occupy consecutive positions within the original sequences. It is used by the diff utility, by Git for reconciling multiple changes, etc. The LCS distance between Strings X (length n) and Y (length m) is n + m - 2 |LCS(X, Y)| min = 0 max = n + m LCS distance is equivalent to Levenshtein distance, when only insertion and deletion is allowed (no substitution), or when the cost of the substitution is the double of the cost of an insertion or deletion. ! This class currently implements the dynamic programming approach, which has a space requirement O(m * n)!

Author:

Thibault Debatty

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
LongestCommonSubsequence()

Method Summary

Modifier and Type	Method and Description
double	distance(String s1, String s2) Return the LCS distance between strings s1 and s2, computed as |s1| + |s2| - 2 * |LCS(s1, s2)|.
int	length(String s1, String s2) Return the length of Longest Common Subsequence (LCS) between strings s1 and s2.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LongestCommonSubsequence

public LongestCommonSubsequence()

Method Detail

distance

public final double distance(String s1,
                             String s2)

Return the LCS distance between strings s1 and s2, computed as |s1| + |s2| - 2 * |LCS(s1, s2)|.

Specified by:

distance in interface StringDistance

Parameters:

s1 - The first string to compare.

s2 - The second string to compare.

Returns:

the LCS distance between strings s1 and s2, computed as |s1| + |s2| - 2 * |LCS(s1, s2)|

Throws:

NullPointerException - if s1 or s2 is null.

length

public final int length(String s1,
                        String s2)

Return the length of Longest Common Subsequence (LCS) between strings s1 and s2.

Parameters:

s1 - The first string to compare.

s2 - The second string to compare.

Returns:

the length of LCS(s1, s2)

Throws:

NullPointerException - if s1 or s2 is null.