Create Bloomfiter.js

Author: ekramzafar

Bloomfiter.js

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+// Define a Bloom filter class
+class BloomFilter {
+  // Constructor takes the size of the bit array and the number of hash functions
+  constructor(size, numHashes) {
+    this.size = size; // The size of the bit array
+    this.numHashes = numHashes; // The number of hash functions
+    this.bitArray = new Array(size).fill(0); // Initialize the bit array with zeros
+  }
+
+  // A simple hash function that takes a string and returns an integer
+  hash(str) {
+    let hash = 0;
+    for (let i = 0; i < str.length; i++) {
+      hash = (hash * 31 + str.charCodeAt(i)) % this.size;
+    }
+    return hash;
+  }
+
+  // A method to generate multiple hashes for a given element
+  // It uses double hashing technique to avoid correlation between hashes
+  generateHashes(element) {
+    let hashes = [];
+    let hash1 = this.hash(element); // First hash
+    let hash2 = this.hash(hash1 + element); // Second hash
+    for (let i = 0; i < this.numHashes; i++) {
+      // Generate more hashes by adding multiples of second hash to first hash
+      let newHash = (hash1 + i * hash2) % this.size;
+      hashes.push(newHash);
+    }
+    return hashes;
+  }
+
+  // A method to add an element to the Bloom filter
+  add(element) {
+    // Generate the hashes for the element
+    let hashes = this.generateHashes(element);
+    // Set the bits at the hashed positions to 1
+    for (let hash of hashes) {
+      this.bitArray[hash] = 1;
+    }
+  }
+
+  // A method to check if an element is in the Bloom filter
+  contains(element) {
+    // Generate the hashes for the element
+    let hashes = this.generateHashes(element);
+    // Check if all the bits at the hashed positions are 1
+    for (let hash of hashes) {
+      if (this.bitArray[hash] === 0) {
+        return false; // Definitely not in the set
+      }
+    }
+    return true; // Probably in the set, but could be a false positive
+  }
+}
+
+// Example usage
+// Create a Bloom filter with size 100 and 3 hash functions
+let bf = new BloomFilter(100, 3);
+
+// Add some elements to the filter
+bf.add("apple");
+bf.add("banana");
+bf.add("cherry");
+
+// Check if some elements are in the filter
+console.log(bf.contains("apple")); // true
+console.log(bf.contains("banana")); // true
+console.log(bf.contains("cherry")); // true
+console.log(bf.contains("durian")); // false
+console.log(bf.contains("elderberry")); // false
+
+// Add more elements to the filter
+bf.add("fig");
+bf.add("grape");
+bf.add("honeydew");
+
+// Check if some elements are in the filter
+console.log(bf.contains("fig")); // true
+console.log(bf.contains("grape")); // true
+console.log(bf.contains("honeydew")); // true
+console.log(bf.contains("iceberg")); // false
+console.log(bf.contains("jackfruit")); // false
+
+// There is a chance of false positives, but not false negatives
+console.log(bf.contains("kiwi")); // false (correct)
+console.log(bf.contains("lime")); // true (false positive)
+// const b = new BloomFilters();
+module.exports = BloomFilters;