optimized mergesort with arrays

manuelkiessling · Apr 11, 2012 · 52e07cc · 52e07cc
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diff --git a/lib/algorithm/mergesortArray.js b/lib/algorithm/mergesortArray.js
@@ -0,0 +1,61 @@
+"use strict";
+if (typeof define !== 'function') { var define = require('amdefine')(module) }
+
+define([], function() {
+
+  var split = function(list) {
+    var halfsize = Math.floor(list.length / 2);
+    var left = list.splice(0, halfsize);
+    var right = list;
+    return {
+      left: left,
+      right: right
+    }
+  };
+
+  var merge = function(left, right, compare) {
+    var merged = [];
+    var leftLength = left.length;
+    var rightLength = right.length;
+    var leftIndex = 0;
+    var rightIndex = 0;
+    while (leftIndex < leftLength && rightIndex < rightLength) {
+      if (compare(left[leftIndex], right[rightIndex]) <= 0) { // item in left is smaller or equal
+        merged.push(left[leftIndex]);
+        leftIndex++;
+      } else {
+        merged.push(right[rightIndex]);
+        rightIndex++;
+      }
+    }
+
+    while (leftIndex < leftLength) {
+      merged.push(left[leftIndex]);
+      leftIndex++;
+    }
+
+    while (rightIndex < rightLength) {
+      merged.push(right[rightIndex]);
+      rightIndex++;
+    }
+
+    return merged;
+  };
+
+  var mergesort = function(list, compare) {
+    if (list.length <= 1) {
+      return list;
+    } else {
+      var sublists = split(list);
+      var sublistleft = sublists.left;
+      var sublistright = sublists.right;
+
+      var left = mergesort(sublistleft, compare);
+      var right = mergesort(sublistright, compare);
+
+      return merge(left, right, compare);
+    }
+  };
+
+  return mergesort;
+});
diff --git a/performance/lib/algorithm/mergesortArray.perf.html b/performance/lib/algorithm/mergesortArray.perf.html
@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Performance/Memory test page for mergesortArray.js</title>
+    <script type="text/javascript" src="../../../vendor/require-1.0.7/require.js"></script>
+  </head>
+
+  <body>
+    <script type="text/javascript">
+      require.config({
+        baseUrl: './'
+      });
+
+      require(['../../../lib/algorithm/mergesortArray.js'], function(mergesort) {
+        var compareNumbers = function(a, b) {
+          if (a < b) {
+            return -1;
+          }
+          if (a === b) {
+            return 0;
+          }
+          if (a > b) {
+            return 1;
+          }
+        };
+
+        var items = [];
+        for (var i = 0; i < 1000000; i++) {
+          items.push(Math.floor(Math.random() * 1000000));
+        }
+
+        var start = new Date().getTime();
+        var sorted = mergesort(items, compareNumbers);
+        var end = new Date().getTime();
+        var time = end - start;
+        window.alert(time);
+      });
+    </script>
+  </body>
+</html>
diff --git a/performance/lib/algorithm/mergesortArray.perf.js b/performance/lib/algorithm/mergesortArray.perf.js
@@ -0,0 +1,39 @@
+"use strict";
+if (typeof define !== 'function') { var define = require('amdefine')(module) }
+
+var compareNumbers = function(a, b) {
+  if (a < b) {
+    return -1;
+  }
+  if (a === b) {
+    return 0;
+  }
+  if (a > b) {
+    return 1;
+  }
+};
+
+define(["../../../lib/datastructure/Queue", "../../../lib/algorithm/mergesortArray"], function(Queue, mergesort) {
+  var compareNumbers = function(a, b) {
+    if (a < b) {
+      return -1;
+    }
+    if (a === b) {
+      return 0;
+    }
+    if (a > b) {
+      return 1;
+    }
+  };
+
+  var items = [];
+  for (var i = 0; i < 10000000; i++) {
+    items.push(Math.floor(Math.random() * 10000000));
+  }
+
+  var start = new Date().getTime();
+  var sorted = mergesort(items, compareNumbers);
+  var end = new Date().getTime();
+  var time = end - start;
+  console.log(time);
+});
diff --git a/spec/algorithm/mergesortArray.spec.js b/spec/algorithm/mergesortArray.spec.js
@@ -0,0 +1,25 @@
+"use strict";
+if (typeof define !== 'function') { var define = require('amdefine')(module) }
+
+var compareNumbers = function(a, b) {
+  if (a < b) {
+    return -1;
+  }
+  if (a === b) {
+    return 0;
+  }
+  if (a > b) {
+    return 1;
+  }
+};
+
+define(["../../lib/algorithm/mergesortArray"], function(mergesort) {
+  describe("mergesort", function() {
+    it("correctly sorts", function() {
+      var unsorted = [4, 9, 7, 8, 1, 9];
+
+      var sorted = mergesort(unsorted, compareNumbers);
+      expect(sorted.join("")).toEqual("147899");
+    });
+  });
+});