Add code for Bloom Filter, tests

Author: Jamil

Bloom Filter/BloomFilter.swift

@@ -0,0 +1,58 @@
+import Foundation
+
+public class BloomFilter<T> {
+    private(set) private var arr: [Bool]
+    private(set) private var hashFunctions: [T -> Int]
+    
+    public init(size: Int = 1024, hashFunctions: [T -> Int]) {
+        self.arr = Array<Bool>(count: size, repeatedValue: false)
+        self.hashFunctions = hashFunctions
+    }
+    
+    private func computeHashes(value: T) -> [Int] {
+        return hashFunctions.map() { hashFunc in
+            abs(hashFunc(value) % self.arr.count)
+        }
+    }
+    
+    public func insert(toInsert: T) {
+        let hashValues: [Int] = self.computeHashes(toInsert)
+        
+        for hashValue in hashValues {
+            self.arr[hashValue] = true
+        }
+    }
+    
+    public func insert(values: [T]) {
+        for value in values {
+            self.insert(value)
+        }
+    }
+    
+    public func query(value: T) -> Bool {
+        let hashValues = self.computeHashes(value)
+        
+        // Map hashes to indices in the Bloom filter
+        let results = hashValues.map() { hashValue in
+            self.arr[hashValue]
+        }
+        
+        // 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, combine: { $0 && $1 })
+        
+        return exists
+    }
+    
+    public func isEmpty() -> Bool {
+        // Reduce list; as soon as the reduction hits a 'true' value, the && condition will fail
+        return arr.reduce(true) { prev, next in
+            prev && !next
+        }
+    }
+    
+}

Bloom Filter/BloomFilterTests/BloomFilterTests.swift

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+import XCTest
+import BloomFilter
+
+/* 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.characters {
+        hash = ((hash << 5) &+ hash) &+ char.hashValue
+    }
+    
+    return Int(hash)
+}
+
+func sdbm(x: String) -> Int {
+    var hash = 0
+    
+    for char in x.characters {
+        hash = char.hashValue &+ (hash << 6) &+ (hash << 16) &- hash;
+    }
+    
+    return Int(hash)
+}
+
+
+class BloomFilterTests: XCTestCase {
+    
+    func testSingleHashFunction() {
+        let bloom = BloomFilter<String>(hashFunctions: [djb2])
+        
+        bloom.insert("Hello world!")
+        
+        let result_good = bloom.query("Hello world!")
+        let result_bad = bloom.query("Hello world")
+        
+        XCTAssertTrue(result_good)
+        XCTAssertFalse(result_bad)
+    }
+    
+    func testEmptyFilter() {
+        let bloom = BloomFilter<String>(hashFunctions: [djb2])
+        
+        let empty = bloom.isEmpty()
+        
+        XCTAssertTrue(empty)
+    }
+    
+    func testMultipleHashFunctions() {
+        let bloom = BloomFilter<String>(hashFunctions: [djb2, sdbm])
+        
+        bloom.insert("Hello world!")
+        
+        let result_good = bloom.query("Hello world!")
+        let result_bad = bloom.query("Hello world")
+        
+        XCTAssertTrue(result_good)
+        XCTAssertFalse(result_bad)
+    }
+    
+    func testFalsePositive() {
+        let bloom = BloomFilter<String>(size: 5, hashFunctions: [djb2, sdbm])
+        
+        bloom.insert(["hello", "elloh", "llohe", "lohel", "ohell"])
+        
+        print("Inserted")
+        
+        let query = bloom.query("This wasn't inserted!")
+        
+        // This is true even though we did not insert the value in the Bloom filter;
+        // the Bloom filter is capable of producing false positives but NOT 
+        // false negatives.
+        
+        XCTAssertTrue(query)
+    }
+}

Bloom Filter/BloomFilterTests/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>en</string>
+	<key>CFBundleExecutable</key>
+	<string>$(EXECUTABLE_NAME)</string>
+	<key>CFBundleIdentifier</key>
+	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>$(PRODUCT_NAME)</string>
+	<key>CFBundlePackageType</key>
+	<string>BNDL</string>
+	<key>CFBundleShortVersionString</key>
+	<string>1.0</string>
+	<key>CFBundleSignature</key>
+	<string>????</string>
+	<key>CFBundleVersion</key>
+	<string>1</string>
+</dict>
+</plist>