Including hashing functions

Author: cutajarj

src/main/java/com/packt/datastructuresandalg/lesson3/hashtable/HashProvider.java

@@ -0,0 +1,5 @@
+package com.packt.datastructuresandalg.lesson3.hashtable;
+
+public interface HashProvider<K> {
+    int hashKey(K key, int tableSize);
+}

src/main/java/com/packt/datastructuresandalg/lesson3/hashtable/HashTable.java

@@ -0,0 +1,9 @@
+package com.packt.datastructuresandalg.lesson3.hashtable;
+
+import java.util.Optional;
+
+public interface HashTable<K,V> {
+    void put(K key,V value);
+
+    Optional<V> get(K key);
+}

src/main/java/com/packt/datastructuresandalg/lesson3/hashtable/MultiplicationHashing.java

@@ -0,0 +1,21 @@
+package com.packt.datastructuresandalg.lesson3.hashtable;
+
+public class MultiplicationHashing implements HashProvider<Integer> {
+    private double k;
+
+    public MultiplicationHashing(double k) {
+        this.k = k;
+    }
+
+    public int hashKey(Integer key, int tableSize) {
+        return (int) (tableSize * (k * key % 1));
+    }
+
+    public static void main(String[] args) {
+        MultiplicationHashing multiplicationHashing = new MultiplicationHashing((Math.sqrt(5) - 1) / 2);
+        System.out.println(multiplicationHashing.hashKey(337481990, 1000));
+        System.out.println(multiplicationHashing.hashKey(116241990, 1000));
+        System.out.println(multiplicationHashing.hashKey(983611990, 1000));
+        System.out.println(multiplicationHashing.hashKey(201031990, 1000));
+    }
+}

src/main/java/com/packt/datastructuresandalg/lesson3/hashtable/RemainderHashing.java

@@ -0,0 +1,21 @@
+package com.packt.datastructuresandalg.lesson3.hashtable;
+
+public class RemainderHashing implements HashProvider<Integer>{
+
+    public int hashKey(Integer key, int tableSize) {
+        return key % tableSize;
+    }
+
+    public static void main(String[] args) {
+        RemainderHashing remainderHashing = new RemainderHashing();
+        System.out.println(remainderHashing.hashKey(337481990, 1000));
+        System.out.println(remainderHashing.hashKey(116241990, 1000));
+        System.out.println(remainderHashing.hashKey(983611990, 1000));
+        System.out.println(remainderHashing.hashKey(201031990, 1000));
+
+        System.out.println(remainderHashing.hashKey(337481990, 1447));
+        System.out.println(remainderHashing.hashKey(116241990, 1447));
+        System.out.println(remainderHashing.hashKey(983611990, 1447));
+        System.out.println(remainderHashing.hashKey(201031990, 1447));
+    }
+}

src/main/java/com/packt/datastructuresandalg/lesson3/hashtable/UniversalHashing.java

@@ -0,0 +1,35 @@
+package com.packt.datastructuresandalg.lesson3.hashtable;
+
+import java.math.BigInteger;
+
+public class UniversalHashing implements HashProvider<Integer> {
+
+    private final BigInteger i, j;
+    private final long p = 47055833459L;
+
+    public UniversalHashing() {
+        j = BigInteger.valueOf((long) (Math.random() * p));
+        i = BigInteger.valueOf(1 + (long) (Math.random() * (p - 1L)));
+    }
+
+    public int hashKey(Integer key, int tableSize) {
+        return i.multiply(BigInteger.valueOf(key)).add(j)
+                .mod(BigInteger.valueOf(p))
+                .mod(BigInteger.valueOf(tableSize))
+                .intValue();
+    }
+
+    public static void main(String[] args) {
+        UniversalHashing universalHashing = new UniversalHashing();
+        System.out.println(universalHashing.hashKey(337481990, 1000));
+        System.out.println(universalHashing.hashKey(116241990, 1000));
+        System.out.println(universalHashing.hashKey(983611990, 1000));
+        System.out.println(universalHashing.hashKey(201031990, 1000));
+
+        universalHashing = new UniversalHashing();
+        System.out.println(universalHashing.hashKey(337481990, 1000));
+        System.out.println(universalHashing.hashKey(116241990, 1000));
+        System.out.println(universalHashing.hashKey(983611990, 1000));
+        System.out.println(universalHashing.hashKey(201031990, 1000));
+    }
+}