Updated starter code for 2018 lab.

580461a3 · Brady James Garvin · 14e416f6 · 580461a3 · 580461a3 · 580461a3
Commit 580461a3 authored Nov 29, 2018 by Brady James Garvin
--- a/index.html
+++ b/index.html
@@ -9,7 +9,8 @@
 </head>

 <body>
-  <div id="result"></div>
+  <div id="time"></div>
+  <div id="freeness"></div>
  <script src="libraries/jquery/jquery.min.js"></script>
  <script src="js/hash_table.js"></script>
  <script src="js/words.js"></script>

--- a/js/hash_table.js
+++ b/js/hash_table.js
@@ -60,6 +60,19 @@ class HashTable {
    return this._size;
  }

+  get collisionFreeness() {
+    if (this._size === 0) {
+      return 1.0;
+    }
+    let occupiedBucketCount = 0;
+    for (const bucket of this._buckets) {
+      if (bucket.length > 0) {
+        ++occupiedBucketCount;
+      }
+    }
+    return occupiedBucketCount / this._size;
+  }
+
  has(element) {
    return this._buckets[this._hashFunction(element)].includes(element);
  }
@@ -68,12 +81,12 @@ class HashTable {
    const bucket = this._buckets[this._hashFunction(element)];
    if (!bucket.includes(element)) {
      bucket.push(element);
-    }
      ++this._size;
      if (this._size / this._buckets.length > MAXIMUM_LOAD_FACTOR) {
        this._resize();
      }
    }
+  }

  delete(element) {
    const bucket = this._buckets[this._hashFunction(element)];

--- a/js/index.js
+++ b/js/index.js
@@ -4,11 +4,19 @@

 const startTime = Date.now();

-const table = new HashTable((word) => 0);
+const table = new HashTable((word) => 0); // TODO: Design a better hash function
+
 for (const word of DICTIONARY) {
  table.add(word);
 }

+for (const word of DICTIONARY) {
+  if (!table.has(word)) {
+    throw new Error(`Found an inconsistency in the hash function when applying it to "${word}"`);
+  }
+}
+
 const endTime = Date.now();

-$('#result').text(`Constructed hash table of American English words in ${endTime - startTime} ms.`);
+$('#time').text(`Constructed and verified a hash table of American English words in ${endTime - startTime} ms.`);
+$('#freeness').text(`Collision freeness using this hash function: ${(100 * table.collisionFreeness).toFixed(3)}%.`);