BloomFilter minor fixes.

Author: trekhleb

src/data-structures/bloom-filter/BloomFilter.js

@@ -1,6 +1,6 @@
 export default class BloomFilter {
   /**
-   * @param {number} size
+   * @param {number} size - the size of the storage.
    */
   constructor(size = 100) {
     // Bloom filter size directly affects the likelihood of false positives.
@@ -15,7 +15,7 @@ export default class BloomFilter {
   insert(item) {
     const hashValues = this.getHashValues(item);
 
-    // Set each hashValue index to true
+    // Set each hashValue index to true.
     hashValues.forEach(val => this.storage.setValue(val));
   }
 
@@ -26,8 +26,8 @@ export default class BloomFilter {
   mayContain(item) {
     const hashValues = this.getHashValues(item);
 
-    for (let i = 0; i < hashValues.length; i += 1) {
-      if (!this.storage.getValue(hashValues[i])) {
+    for (let hashIndex = 0; hashIndex < hashValues.length; hashIndex += 1) {
+      if (!this.storage.getValue(hashValues[hashIndex])) {
         // We know that the item was definitely not inserted.
         return false;
       }
@@ -50,7 +50,7 @@ export default class BloomFilter {
     const storage = [];
 
     // Initialize all indexes to false
-    for (let i = 0; i < size; i += 1) {
+    for (let storageCellIndex = 0; storageCellIndex < size; storageCellIndex += 1) {
       storage.push(false);
     }
 
@@ -67,14 +67,14 @@ export default class BloomFilter {
   }
 
   /**
-   * @param {string} str
+   * @param {string} item
    * @return {number}
    */
-  hash1(str) {
+  hash1(item) {
     let hash = 0;
 
-    for (let i = 0; i < str.length; i += 1) {
-      const char = str.charCodeAt(i);
+    for (let charIndex = 0; charIndex < item.length; charIndex += 1) {
+      const char = item.charCodeAt(charIndex);
       hash = (hash << 5) + hash + char;
       hash &= hash; // Convert to 32bit integer
       hash = Math.abs(hash);
@@ -84,44 +84,48 @@ export default class BloomFilter {
   }
 
   /**
-   * @param {string} str
+   * @param {string} item
    * @return {number}
    */
-  hash2(str) {
+  hash2(item) {
     let hash = 5381;
 
-    for (let i = 0; i < str.length; i += 1) {
-      const char = str.charCodeAt(i);
+    for (let charIndex = 0; charIndex < item.length; charIndex += 1) {
+      const char = item.charCodeAt(charIndex);
       hash = (hash << 5) + hash + char; /* hash * 33 + c */
     }
 
-    return hash % this.size;
+    return Math.abs(hash % this.size);
   }
 
   /**
-   * @param {string} str
+   * @param {string} item
    * @return {number}
    */
-  hash3(str) {
+  hash3(item) {
     let hash = 0;
 
-    for (let i = 0; i < str.length; i += 1) {
-      const char = str.charCodeAt(i);
+    for (let charIndex = 0; charIndex < item.length; charIndex += 1) {
+      const char = item.charCodeAt(charIndex);
       hash = (hash << 5) - hash;
       hash += char;
       hash &= hash; // Convert to 32bit integer
     }
 
-    return hash % this.size;
+    return Math.abs(hash % this.size);
   }
 
   /**
-   * Runs all 3 hash functions on the input and returns an array of results
+   * Runs all 3 hash functions on the input and returns an array of results.
    *
-   * @param {string} str
+   * @param {string} item
    * @return {number[]}
    */
   getHashValues(item) {
-    return [this.hash1(item), Math.abs(this.hash2(item)), Math.abs(this.hash3(item))];
+    return [
+      this.hash1(item),
+      this.hash2(item),
+      this.hash3(item),
+    ];
   }
 }

src/data-structures/bloom-filter/__test__/BloomFilter.test.js

@@ -1,39 +1,62 @@
 import BloomFilter from '../BloomFilter';
 
-describe('Bloom Filter', () => {
+describe('BloomFilter', () => {
   let bloomFilter;
-  const people = ['Bruce Wayne', 'Clark Kent', 'Barry Allen'];
+  const people = [
+    'Bruce Wayne',
+    'Clark Kent',
+    'Barry Allen',
+  ];
 
   beforeEach(() => {
     bloomFilter = new BloomFilter();
   });
 
-  it('Should have methods named "insert" and "mayContain"', () => {
+  it('should have methods named "insert" and "mayContain"', () => {
     expect(typeof bloomFilter.insert).toBe('function');
     expect(typeof bloomFilter.mayContain).toBe('function');
   });
 
-  it('Should create a new filter store with the appropriate methods', () => {
+  it('should create a new filter store with the appropriate methods', () => {
     const store = bloomFilter.createStore(18);
     expect(typeof store.getValue).toBe('function');
     expect(typeof store.setValue).toBe('function');
   });
 
-  it('Should hash deterministically with all 3 hash functions', () => {
-    const str = 'abc';
-    expect(bloomFilter.hash1(str)).toEqual(bloomFilter.hash1(str));
-    expect(bloomFilter.hash2(str)).toEqual(bloomFilter.hash2(str));
-    expect(bloomFilter.hash3(str)).toEqual(bloomFilter.hash3(str));
+  it('should hash deterministically with all 3 hash functions', () => {
+    const str1 = 'apple';
+
+    expect(bloomFilter.hash1(str1)).toEqual(bloomFilter.hash1(str1));
+    expect(bloomFilter.hash2(str1)).toEqual(bloomFilter.hash2(str1));
+    expect(bloomFilter.hash3(str1)).toEqual(bloomFilter.hash3(str1));
+
+    expect(bloomFilter.hash1(str1)).toBe(14);
+    expect(bloomFilter.hash2(str1)).toBe(43);
+    expect(bloomFilter.hash3(str1)).toBe(10);
+
+    const str2 = 'orange';
+
+    expect(bloomFilter.hash1(str2)).toEqual(bloomFilter.hash1(str2));
+    expect(bloomFilter.hash2(str2)).toEqual(bloomFilter.hash2(str2));
+    expect(bloomFilter.hash3(str2)).toEqual(bloomFilter.hash3(str2));
+
+    expect(bloomFilter.hash1(str2)).toBe(0);
+    expect(bloomFilter.hash2(str2)).toBe(61);
+    expect(bloomFilter.hash3(str2)).toBe(10);
   });
 
-  it('Should create an array with 3 hash values', () => {
-    expect(bloomFilter.getHashValues('abc').length).toEqual(3);
+  it('should create an array with 3 hash values', () => {
+    expect(bloomFilter.getHashValues('abc').length).toBe(3);
+    expect(bloomFilter.getHashValues('abc')).toEqual([66, 63, 54]);
   });
 
-  it('Should insert strings correctly and return true when checking for inserted values', () => {
+  it('should insert strings correctly and return true when checking for inserted values', () => {
     people.forEach(person => bloomFilter.insert(person));
-    expect(bloomFilter.mayContain('Bruce Wayne')).toBe(true);
-    expect(bloomFilter.mayContain('Clark Kent')).toBe(true);
-    expect(bloomFilter.mayContain('Barry Allen')).toBe(true);
+
+    expect(bloomFilter.mayContain('Bruce Wayne')).toBeTruthy();
+    expect(bloomFilter.mayContain('Clark Kent')).toBeTruthy();
+    expect(bloomFilter.mayContain('Barry Allen')).toBeTruthy();
+
+    expect(bloomFilter.mayContain('Tony Stark')).toBeFalsy();
   });
 });