Merge pull request #162 from knaxus/bloom-filters

Bloom filters

Author: ashokdey

TOC.md

@@ -50,6 +50,8 @@
     - [K Largest Elements](src/_DataStructures_/Heaps/k-largest-in-array)
     - [K Smallest Elements](src/_DataStructures_/Heaps/k-smallest-in-array)
 - [Hash Table](src/_DataStructures_/HashTable)
+- [Set](src/_DataStructures_/Set)
+- [Bloom Filters](src/_DataStructures_/BloomFilters)
 
 ### Logical Problems
 

src/_DataStructures_/BloomFilters/index.js

@@ -0,0 +1,97 @@
+class BloomFilters {
+  constructor(size = 101) {
+    this.size = size;
+    this.data = this.getStorage(size);
+  }
+
+  add(element) {
+    const indices = this.getIndices(element);
+
+    for (let i = 0; i < indices.length; i += 1) {
+      this.data.setBit(indices[i]);
+    }
+  }
+
+  contains(element) {
+    const indices = this.getIndices(element);
+
+    for (let i = 0; i < indices.length; i += 1) {
+      const index = indices[i];
+      if (!this.data.getBit(index)) {
+        return false; // item is definately not there
+      }
+    }
+    return true; // item may be there
+  }
+
+  getIndices(element) {
+    return [this.hashOne(element), this.hashTwo(element), this.hashThree(element)];
+  }
+
+  hashOne(value) {
+    const stringValue = String(value);
+    let hashVal = 0;
+
+    for (let i = 0; i < stringValue.length; i += 1) {
+      hashVal += stringValue.charCodeAt(i) - 96;
+    }
+
+    // eslint-disable-next-line no-bitwise
+    hashVal &= hashVal;
+
+    return Math.abs(hashVal % this.size);
+  }
+
+  hashTwo(value) {
+    const stringValue = String(value);
+    const PRIME_MULTIPLIER = 1801; // Random prime number
+    let hashVal = 0;
+
+    for (let i = 0; i < stringValue.length; i += 1) {
+      hashVal += stringValue.charCodeAt(i) - 96;
+      hashVal *= PRIME_MULTIPLIER;
+    }
+
+    return Math.abs(hashVal % this.size);
+  }
+
+  hashThree(value) {
+    const stringValue = String(value);
+    const PRIME_MULTIPLIER = 1801; // Random prime number
+    const PRIME_ADDER = 2029; // Random prime number
+    let hashVal = 0;
+
+    for (let i = 0; i < stringValue.length; i += 1) {
+      hashVal += stringValue.charCodeAt(i) - 96;
+      hashVal *= PRIME_MULTIPLIER;
+      hashVal += PRIME_ADDER;
+    }
+    // eslint-disable-next-line no-bitwise
+    hashVal &= hashVal;
+    return Math.abs(hashVal % this.size);
+  }
+
+  // eslint-disable-next-line class-methods-use-this
+  getStorage(size) {
+    const data = new Array(size).fill(0);
+
+    return {
+      setBit(index) {
+        data[index] = 1;
+      },
+      getBit(index) {
+        return data[index];
+      },
+    };
+  }
+}
+
+// const b = new BloomFilters();
+
+// b.add('React.js');
+// b.add('Node.js');
+
+// console.log(b.contains('JavaScript'));
+// console.log(b.contains('React.js'));
+
+module.exports = BloomFilters;

src/_DataStructures_/HashTable/index.js

@@ -11,15 +11,15 @@ class HashTable {
     this.threshold = 0.7;
     // the main bucket
     this.bucket = new Array(this.slot);
+    // fill the bucket with null
+    // for (let i = 0; i < this.slot; i += 1) this.bucket[i] = null;
+    this.bucket.fill(null);
     this.allowResize = allowResize;
     this.strongHash = strongHash;
     if (custonHash) {
       // eslint-disable-next-line no-underscore-dangle
       this._hash = custonHash;
     }
-
-    // fill the bucket with null
-    for (let i = 0; i < this.slot; i += 1) this.bucket[i] = null;
   }
 
   _hash(key) {
@@ -36,12 +36,14 @@ class HashTable {
     for (let i = 0; i < loopTill; i += 1) {
       const char = stringKey[i];
       const value = char.charCodeAt(0) - 96;
-      index = (index * PRIME_MULTIPLIER + value) % this.bucket.length;
+      // eslint-disable-next-line no-bitwise
+      index &= index;
+      index = index * PRIME_MULTIPLIER + value;
       if (this.strongHash) {
-        index = (index + PRIME_ADDER) % this.bucket.length;
+        index += PRIME_ADDER;
       }
     }
-    return index;
+    return Math.abs(index % this.bucket.length);
   }
 
   _resize() {

src/_DataStructures_/Set/index.js

@@ -0,0 +1,77 @@
+// XSet because ES6 already has a Set class
+class XSet {
+  constructor() {
+    this.data = this.getStore();
+  }
+
+  add(element) {
+    this.data.push(element);
+  }
+
+  remove(element) {
+    this.data.pop(element);
+  }
+
+  has(element) {
+    return this.data.contains(element);
+  }
+
+  values() {
+    return this.data.val();
+  }
+
+  union(givenSet) {
+    const result = new Set();
+    const firstSetValues = this.values();
+    const givenSetValues = givenSet.values();
+
+    // eslint-disable-next-line no-restricted-syntax
+    for (const e of firstSetValues) result.add(e);
+
+    // eslint-disable-next-line no-restricted-syntax
+    for (const e of givenSetValues) result.add(e);
+
+    return result;
+  }
+
+  // eslint-disable-next-line class-methods-use-this
+  getStore() {
+    const store = {};
+
+    return {
+      push(el) {
+        if (!store[el]) {
+          store[el] = true;
+        }
+      },
+      pop(el) {
+        if (store[el]) {
+          delete store[el];
+        }
+      },
+      contains(el) {
+        return !!store[el];
+      },
+      val() {
+        return Object.keys(store);
+      },
+    };
+  }
+}
+
+// const s = new XSet();
+
+// s.add(10);
+// s.add(20);
+// s.add(90);
+
+// console.log(s.has(1));
+// console.log(s.has(10));
+// console.log(s.has(90));
+
+// console.log(s.values());
+// s.remove(90);
+// console.log(s.has(90));
+// console.log(s.data);
+
+module.exports = XSet;