Small fixes, proper example

Author: MpoMp

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

@@ -51,24 +51,27 @@ public final class OptimalStringAlignment implements StringDistance {
      * @return the OSA distance
      */
     public final double distance(final String s1, final String s2) {
+        int n = s1.length(), m = s2.length();
+        if (n == 0) return m;
+        if (m == 0) return n;
+        
 
         // Create the distance matrix H[0 .. s1.length+1][0 .. s2.length+1]
         int[][] d = new int[s1.length() + 2][s2.length() + 2];
 
-        //@TODO: check special cases
         //initialize top row and leftmost column
-        for (int i = 0; i <= s1.length(); i++) {
+        for (int i = 0; i <= n; i++) {
             d[i][0] = i;
         }
-        for (int j = 0; j <= s2.length(); j++) {
+        for (int j = 0; j <= m; j++) {
             d[0][j] = j;
         }
 
         //fill the distance matrix
         int cost;
 
-        for (int i = 1; i <= s1.length(); i++) {
-            for (int j = 1; j <= s2.length(); j++) {
+        for (int i = 1; i <= n; i++) {
+            for (int j = 1; j <= m; j++) {
 
                 //if s1[i - 1] = s2[j - 1] then cost = 0, else cost = 1
                 cost = (s1.charAt(i - 1) == s2.charAt(j - 1)) ? 0 : 1;
@@ -77,16 +80,19 @@ public final double distance(final String s1, final String s2) {
                         d[i - 1][j - 1] + cost, // substitution
                         d[i][j - 1] + 1, // insertion
                         d[i - 1][j] + 1 // deletion
-                        );
-                
+                );
+
                 //transposition check
-                if (i > 1 && j > 1 && s1.charAt(i-1) == s2.charAt(j-2) && s1.charAt(i-2) == s2.charAt(j-1)){
-                    d[i][j] = Math.min(d[i][j], d[i-2][j-2] + cost);
+                if (i > 1 && j > 1 
+                        && s1.charAt(i - 1) == s2.charAt(j - 2) 
+                        && s1.charAt(i - 2) == s2.charAt(j - 1)
+                    ){
+                    d[i][j] = Math.min(d[i][j], d[i - 2][j - 2] + cost);
                 }
             }
         }
 
-        return d[s1.length() + 1][s2.length() + 1];
+        return d[n][m];
     }
 
     private static int min(

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

@@ -122,21 +122,9 @@ public static void main(String[] args) {
         System.out.println("\nOptimal String Alignment");
         OptimalStringAlignment osa = new OptimalStringAlignment();
 
-        // 1 substitution
-        System.out.println(osa.distance("ABCDEF", "ABDCEF"));
-
-        // 2 substitutions
-        System.out.println(osa.distance("ABCDEF", "BACDFE"));
-
-        // 1 deletion
-        System.out.println(osa.distance("ABCDEF", "ABCDE"));
-        System.out.println(osa.distance("ABCDEF", "BCDEF"));
-
-        System.out.println(osa.distance("ABCDEF", "ABCGDEF"));
-
-        // All different
-        System.out.println(osa.distance("ABCDEF", "POIU"));
-
+        System.out.println(osa.distance("CA", "ABC"));
+        
+        
         // Longest Common Subsequence
         // ==========================
         System.out.println("\nLongest Common Subsequence");