Merge pull request mgechev#87 from deniskyashif/levenshtein-distance-tuning-and-tests

mgechev · mgechev · commit a88c0b95907f · 2015-09-05T17:46:59.000+03:00
Optimized Levenshtein distance algorithm and added unit tests.
diff --git a/src/others/levenshtein-distance.js b/src/others/levenshtein-distance.js
@@ -3,22 +3,31 @@
 
   var levenshteinDistance = (function () {
 
-    function levenshteinDistance(s, ls, t, lt) {
-      if (ls === 0) {
-        return lt;
-      }
-      if (lt === 0) {
-        return ls;
+    function levenshteinDistance (s, ls, t, lt) {
+      var memo = [];
+      var currRowMemo;
+      var i;
+      var k;
+
+      for (k = 0; k <= lt; k += 1) {
+        memo[k] = k;
       }
-      var cost;
-      if (s[ls - 1] === t[lt - 1]) {
-        cost = 0;
-      } else {
-        cost = 1;
+
+      for (i = 1; i <= ls; i += 1) {
+        currRowMemo = [i];
+
+        for (k = 1; k <= lt; k += 1) {
+          currRowMemo[k] = Math.min(
+            currRowMemo[k - 1] + 1,
+            memo[k] + 1,
+            memo[k - 1] + (s[i - 1] !== t[k - 1] ? 1 : 0)
+          );
+        }
+
+        memo = currRowMemo;
       }
-      return Math.min(levenshteinDistance(s, ls - 1, t,     lt) + 1,
-                      levenshteinDistance(s, ls,     t, lt - 1) + 1,
-                      levenshteinDistance(s, ls - 1, t, lt - 1) + cost);
+
+      return memo[lt];
     }
 
     /**
@@ -49,3 +58,4 @@
   exports.levenshteinDistance = levenshteinDistance;
 
 }(typeof exports === 'undefined' ? window : exports));
+
diff --git a/test/others/levenshtein-distance.spec.js b/test/others/levenshtein-distance.spec.js
@@ -0,0 +1,58 @@
+'use strict';
+
+var mod = require('../../src/others/levenshtein-distance.js');
+var levenshteinDistance = mod.levenshteinDistance;
+
+describe('Levenstein\'s minimum edit distance algorithm', function () {
+  it('should be defined', function () {
+    expect(levenshteinDistance).toBeDefined();
+  });
+
+  it('"" -> "" should return 0.', function () {
+    expect(levenshteinDistance('', '')).toBe(0);
+  });
+
+  it('"T" -> "" should return 1.', function () {
+    expect(levenshteinDistance('T', '')).toBe(1);
+  });
+
+  it('"cake" -> "rake" should return 1.', function () {
+    expect(levenshteinDistance('cake', 'rake')).toBe(1);
+  });
+
+  it('"Sofia" -> "Sof" should return 2.', function () {
+    expect(levenshteinDistance('Sofia', 'Sof')).toBe(2);
+  });
+
+  it('"kitten" -> "sitting" should return 3', function () {
+    expect(levenshteinDistance('kitten', 'sitting')).toBe(3);
+  });
+
+  it('"google" -> "lookat" should return 4.', function () {
+    expect(levenshteinDistance('google', 'lookat')).toBe(4);
+  });
+
+  it('"emacs" -> "vim" should return 5.', function () {
+    expect(levenshteinDistance('emacs', 'vim')).toBe(5);
+  });
+
+  it('"coffee" -> "cocoa" should return 4.', function () {
+    expect(levenshteinDistance('coffee', 'cocoa')).toBe(4);
+  });
+
+  it('"Munich" -> "Muenchen" should return 4.', function () {
+    expect(levenshteinDistance('Munich', 'Muenchen')).toBe(4);
+  });
+
+  it('"rosebud" -> "budrose" should return 6.', function () {
+    expect(levenshteinDistance('rosebud', 'budrose')).toBe(6);
+  });
+
+  it('"decided" -> "decisive" should return 4.', function () {
+    expect(levenshteinDistance('decided', 'decisive')).toBe(4);
+  });
+
+  it('"similar" -> "simile" should return 2.', function () {
+    expect(levenshteinDistance('similar', 'simile')).toBe(2);
+  });
+});
