From f737a1c41088fc0ce051098ebd3988d21856534c Mon Sep 17 00:00:00 2001
From: ekramzafar <133132379+ekramzafar@users.noreply.github.com>
Date: Mon, 16 Oct 2023 16:39:45 +0530
Subject: [PATCH] Create Bloomfiter.js
---
Bloomfiter.js | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 89 insertions(+)
create mode 100644 Bloomfiter.js
diff --git a/Bloomfiter.js b/Bloomfiter.js
new file mode 100644
index 0000000..062fc74
--- /dev/null
+++ b/Bloomfiter.js
@@ -0,0 +1,89 @@
+// 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;