Added MetricLCS distance

Author: tdebatty

README.md

@@ -249,11 +249,34 @@ public class MyApp {
 }
 ```
 
-## Metric Longest Common Subsequence
-tbd
-
+## Metric LCS (Longest Common Subsequence)
+Distance metric based on Longest Common Subsequence, from the notes "An LCS-based string metric" by Daniel Bakkelund.
 http://heim.ifi.uio.no/~danielry/StringMetric.pdf
 
+The distance is computed as 1 - |LCS(s1, s2)| / max(|s1|, |s2|)
+```java
+public class MyApp {
+
+        public static void main(String[] args) {
+
+        info.debatty.java.stringsimilarity.MetricLCS lcs = 
+                new info.debatty.java.stringsimilarity.MetricLCS();
+
+        String s1 = "ABCDEFG";   
+        String s2 = "ABCDEFHJKL";
+        // LCS: ABCDEF => length = 6
+        // longest = s2 => length = 10
+        // => 1 - 6/10 = 0.4
+        System.out.println(lcs.distance(s1, s2));
+
+        // LCS: ABDF => length = 4
+        // longest = ABDEF => length = 5
+        // => 1 - 4 / 5 = 0.2
+        System.out.println(lcs.distance("ABDEF", "ABDIF"));
+    }
+}
+```
+
 ## N-Gram distance (Kondrak)
 
 Normalized N-Gram distance as defined by Kondrak, "N-Gram Similarity and Distance", String Processing and Information Retrieval, Lecture Notes in Computer Science Volume 3772, 2005, pp 115-126.

src/main/java/info/debatty/java/stringsimilarity/LongestCommonSubsequence.java

@@ -40,10 +40,24 @@ public static void main(String[] args) {
     }
 
 
+    /**
+     * Return the LCS distance between strings s1 and s2, 
+     * computed as |s1| + |s2| - 2 * |LCS(s1, s2)|
+     * @param s1
+     * @param s2
+     * @return 
+     */
     public double distance(String s1, String s2) {
         return s1.length() + s2.length() - 2 * length(s1, s2);
     }
 
+    /**
+     * Return the length of Longest Common Subsequence (LCS) between strings s1
+     * and s2.
+     * @param s1
+     * @param s2
+     * @return 
+     */
     protected int length(String s1, String s2) {
         /* function LCSLength(X[1..m], Y[1..n])
             C = array(0..m, 0..n)

src/main/java/info/debatty/java/stringsimilarity/MetricLCS.java

@@ -0,0 +1,51 @@
+/*
+ * The MIT License
+ *
+ * Copyright 2015 Thibault Debatty.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package info.debatty.java.stringsimilarity;
+
+import info.debatty.java.stringsimilarity.interfaces.MetricStringDistance;
+import info.debatty.java.stringsimilarity.interfaces.NormalizedStringDistance;
+
+/**
+ * Distance metric based on Longest Common Subsequence, from the notes "An 
+ * LCS-based string metric" by Daniel Bakkelund.
+ * @author Thibault Debatty
+ */
+public class MetricLCS implements MetricStringDistance, NormalizedStringDistance {
+
+    private final LongestCommonSubsequence lcs = new LongestCommonSubsequence();
+    
+    /**
+     * Distance metric based on Longest Common Subsequence, computed as 
+     * 1 - |LCS(s1, s2)| / max(|s1|, |s2|)
+     * @param s1
+     * @param s2
+     * @return 
+     */
+    public double distance(String s1, String s2) {
+        return 1.0 - ((double) lcs.length(s1, s2)) / Math.max(s1.length(), s2.length());
+                
+    }
+    
+}

src/main/java/info/debatty/java/stringsimilarity/examples/MetricLCS.java

@@ -0,0 +1,51 @@
+/*
+ * The MIT License
+ *
+ * Copyright 2015 Thibault Debatty.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package info.debatty.java.stringsimilarity.examples;
+
+/**
+ *
+ * @author Thibault Debatty
+ */
+public class MetricLCS {
+
+        public static void main(String[] args) {
+        
+        info.debatty.java.stringsimilarity.MetricLCS lcs = 
+                new info.debatty.java.stringsimilarity.MetricLCS();
+        
+        String s1 = "ABCDEFG";   
+        String s2 = "ABCDEFHJKL";
+        // LCS: ABCDEF => length = 6
+        // longest = s2 => length = 10
+        // => 1 - 6/10 = 0.4
+        System.out.println(lcs.distance(s1, s2));
+        
+        // LCS: ABDF => length = 4
+        // longest = ABDEF => length = 5
+        // => 1 - 4 / 5 = 0.2
+        System.out.println(lcs.distance("ABDEF", "ABDIF"));
+    }
+    
+}