Apply insertion and deletion weights to empty strings

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

@@ -93,11 +93,19 @@ public final double distance(final String s1, final String s2,
         }
 
         if (s1.length() == 0) {
-            return s2.length();
+            double cost = 0;
+            for (int i = 0; i < s2.length(); i++) {
+                cost += insertionCost(s2.charAt(i));
+            }
+            return cost;
         }
 
         if (s2.length() == 0) {
-            return s1.length();
+            double cost = 0;
+            for (int i = 0; i < s1.length(); i++) {
+                cost += deletionCost(s1.charAt(i));
+            }
+            return cost;
         }
 
         // create two work vectors of floating point (i.e. weighted) distances

src/test/java/info/debatty/java/stringsimilarity/WeightedLevenshteinTest.java

@@ -96,4 +96,28 @@ public double insertionCost(char c) {
 
         NullEmptyTests.testDistance(instance);
     }
+
+    @Test
+    public void emptyStringsUseCharacterInsertionCosts() {
+        WeightedLevenshtein distance = weightedDistance();
+        assertEquals(2.5, distance.distance("", "ab"), 0.000001);
+        assertEquals(2.5, distance.distance("", "ab", Double.MAX_VALUE), 0.000001);
+    }
+
+    @Test
+    public void emptyStringsUseCharacterDeletionCosts() {
+        WeightedLevenshtein distance = weightedDistance();
+        assertEquals(4.75, distance.distance("ab", ""), 0.000001);
+        assertEquals(4.75, distance.distance("ab", "", Double.MAX_VALUE), 0.000001);
+    }
+
+    private WeightedLevenshtein weightedDistance() {
+        return new WeightedLevenshtein(new CharacterSubstitutionInterface() {
+            public double cost(char a, char b) { return 1.0; }
+        }, new CharacterInsDelInterface() {
+            public double insertionCost(char c) { return c == 'a' ? 0.5 : 2.0; }
+            public double deletionCost(char c) { return c == 'a' ? 0.75 : 4.0; }
+        });
+    }
+
 }