Improved Bloom Filter with error handling

This commit includes an improved version of the Bloom filter code, which now includes error handling to check if the number of hash functions passed is greater than the size of the array and raises a fatal error if that's the case. The class now imports foundation library

Author: CHIRAGGARORA

Bloom Filter/BloomFilter.playground/Contents.swift

@@ -1,82 +1,84 @@
 //: Playground - noun: a place where people can play
-
-public class BloomFilter<T> {
-  fileprivate var array: [Bool]
-  private var hashFunctions: [(T) -> Int]
-
-  public init(size: Int = 1024, hashFunctions: [(T) -> Int]) {
-    self.array = [Bool](repeating: false, count: size)
-    self.hashFunctions = hashFunctions
-  }
-
-  private func computeHashes(_ value: T) -> [Int] {
-    return hashFunctions.map { hashFunc in abs(hashFunc(value) % array.count) }
-  }
-
-  public func insert(_ element: T) {
-    for hashValue in computeHashes(element) {
-      array[hashValue] = true
+import Foundation
+
+public class BloomFilter<T: Hashable> {
+    fileprivate var array: [Bool]
+    private var hashFunctions: [(T) -> Int]
+
+    public init(size: Int = 1024, hashFunctions: [(T) -> Int]) {
+        if (hashFunctions.count > size) {
+            fatalError("Number of hash functions should be less than or equal to size of array")
+        }
+        self.array = [Bool](repeating: false, count: size)
+        self.hashFunctions = hashFunctions
     }
-  }
 
-  public func insert(_ values: [T]) {
-    for value in values {
-      insert(value)
+    private func computeHashes(_ value: T) -> [Int] {
+        return hashFunctions.map { hashFunc in abs(hashFunc(value) % array.count) }
     }
-  }
 
-  public func query(_ value: T) -> Bool {
-    let hashValues = computeHashes(value)
+    public func insert(_ element: T) {
+        for hashValue in computeHashes(element) {
+            array[hashValue] = true
+        }
+    }
 
-    // Map hashes to indices in the Bloom Filter
-    let results = hashValues.map { hashValue in array[hashValue] }
+    public func insert(_ values: [T]) {
+        for value in values {
+            insert(value)
+        }
+    }
 
-    // All values must be 'true' for the query to return true
+    public func query(_ value: T) -> Bool {
+        let hashValues = computeHashes(value)
 
-    // This does NOT imply that the value is in the Bloom filter,
-    // only that it may be. If the query returns false, however,
-    // you can be certain that the value was not added.
+        // Map hashes to indices in the Bloom Filter
+        let results = hashValues.map { hashValue in array[hashValue] }
 
-    let exists = results.reduce(true, { $0 && $1 })
-    return exists
-  }
+        // All values must be 'true' for the query to return true
+        // This does NOT imply that the value is in the Bloom filter,
+        // only that it may be. If the query returns false, however,
+        // you can be certain that the value was not added.
+        let exists = results.reduce(true, { $0 && $1 })
+        return exists
+    }
 
-  public func isEmpty() -> Bool {
-    // As soon as the reduction hits a 'true' value, the && condition will fail.
-    return array.reduce(true) { prev, next in prev && !next }
-  }
+    public func isEmpty() -> Bool {
+        // As soon as the reduction hits a 'true' value, the && condition will fail.
+        return array.reduce(true) { prev, next in prev && !next }
+    }
 }
 
 /* Two hash functions, adapted from http://www.cse.yorku.ca/~oz/hash.html */
 
 func djb2(x: String) -> Int {
-  var hash = 5381
-  for char in x {
-    hash = ((hash << 5) &+ hash) &+ char.hashValue
-  }
-  return Int(hash)
+    var hash = 5381
+    for char in x {
+        hash = ((hash << 5) &+ hash) &+ char.hashValue
+    }
+    return Int(hash)
 }
 
 func sdbm(x: String) -> Int {
-  var hash = 0
-  for char in x {
-    hash = char.hashValue &+ (hash << 6) &+ (hash << 16) &- hash
-  }
-  return Int(hash)
+    var hash = 0
+    for char in x {
+        hash = char.hashValue &+ (hash << 6) &+ (hash << 16) &- hash
+    }
+    return Int(hash)
 }
 
 /* A simple test */
-
 let bloom = BloomFilter<String>(size: 17, hashFunctions: [djb2, sdbm])
 
 bloom.insert("Hello world!")
 print(bloom.array)
 
-bloom.query("Hello world!")    // true
-bloom.query("Hello WORLD")     // false
+(bloom.query("Hello world!"))    // true
+(bloom.query("Hello WORLD"))     // false
 
 bloom.insert("Bloom Filterz")
-print(bloom.array)
+(bloom.array)
+
+(bloom.query("Bloom Filterz"))   // true
+(bloom.query("Hello WORLD"))     // false
 
-bloom.query("Bloom Filterz")   // true
-bloom.query("Hello WORLD")     // true