Pages

Tuesday, 14 February 2017

Chapter 27 Exercise 5, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

27.5 (Implement MyHashSet using MyHashMap ) Implement MyHashSet using
MyHashMap . Note that you can create entries with ( key, key ), rather than ( key, value ).


import java.util.Iterator;
import java.util.LinkedList;
import java.util.Set;

public class Exercise05 {

 public static void main(String[] args) {
  MyHashSet<String> set = new MyHashSet<String>();
  set.add("Smith");
  set.add("Anderson");
  set.add("Lewis");
  set.add("Cook");
  set.add("Smith");

  System.out.println("Elements in set: " + set);
  System.out.println("Number of elements in set: " + set.size());
  System.out.println("Is Smith in set? " + set.contains("Smith"));

  set.remove("Smith");
  System.out.print("Names in set in uppercase are ");

  for (String s : set)
   System.out.print(s.toUpperCase() + " ");

  set.clear();
  System.out.println("\nElements in set: " + set);
 }

 static class MyHashSet<E> extends MyHashMap<E, E> implements Iterable<E> {
  /** Remove all elements from this set */
  public void clear() {
   super.clear();
  }

  /** Return true if the element is in the set */
  public boolean contains(E e) {
   return super.containsKey(e);
  }

  /** Add an element to the set */
  public boolean add(E e) {
   if (super.containsKey(e)) {
    return false;
   } else {
    super.put(e, e);
    return true;
   }
  }

  /** Remove the element from the set */
  public boolean remove(E e) {
   if (!super.containsKey(e)) {
    return false;
   } else {
    super.removeOne(e);
    return true;
   }
  }

  /** Return true if the set contains no elements */
  public boolean isEmpty() {
   return super.isEmpty();
  }

  /** Return the number of elements in the set */
  public int size() {
   return super.size();
  }

  /** Return an iterator for the elements in this set */
  public java.util.Iterator<E> iterator() {
   return new MapIterator<E>();
  }

  private class MapIterator<T> implements Iterator<T> {
   private Set<T> values;
   Iterator<T> it;

   @SuppressWarnings("unchecked")
   public MapIterator() {
    values = (Set<T>) keySet();
    it = values.iterator();
   }

   @Override
   public boolean hasNext() {
    return it.hasNext();
   }

   @Override
   public T next() {
    return it.next();
   }

   @Override
   public void remove() {
    throw new UnsupportedOperationException("Remove not allowed!");
   }
  }
  
  @Override
  public String toString() {
   String result = "[";
   for (E e : this) {
    result += e + ", ";
   }
   if(result.length() > 1) {
    result = result.substring(0, result.length() - 2);
   }
   return result + "]";
  }
 }

 static class MyHashMap<K, V> implements MyMap<K, V> {
  // Define the default hash table size. Must be a power of 2
  private static int DEFAULT_INITIAL_CAPACITY = 4;

  // Define the maximum hash table size. 1 << 30 is same as 2^30
  private static int MAXIMUM_CAPACITY = 1 << 30;

  // Current hash table capacity. Capacity is a power of 2
  private int capacity;

  // Define default load factor
  private static float DEFAULT_MAX_LOAD_FACTOR = 0.75f;

  // Specify a load factor used in the hash table
  private float loadFactorThreshold;

  // The number of entries in the map
  private int size = 0;

  // Hash table is an array with each cell that is a linked list
  LinkedList<MyMap.Entry<K, V>>[] table;

  /** Construct a map with the default capacity and load factor */
  public MyHashMap() {
   this(DEFAULT_INITIAL_CAPACITY, DEFAULT_MAX_LOAD_FACTOR);
  }

  /**
   * Construct a map with the specified initial capacity and default load
   * factor
   */
  public MyHashMap(int initialCapacity) {
   this(initialCapacity, DEFAULT_MAX_LOAD_FACTOR);
  }

  /**
   * Construct a map with the specified initial capacity and load factor
   */
  @SuppressWarnings("unchecked")
  public MyHashMap(int initialCapacity, float loadFactorThreshold) {
   if (initialCapacity > MAXIMUM_CAPACITY)
    this.capacity = MAXIMUM_CAPACITY;
   else
    this.capacity = trimToPowerOf2(initialCapacity);

   this.loadFactorThreshold = loadFactorThreshold;
   table = new LinkedList[capacity];
  }

  @Override
  /** Remove all of the entries from this map */
  public void clear() {
   size = 0;
   removeEntries();
  }

  @Override
  /** Return true if the specified key is in the map */
  public boolean containsKey(K key) {
   if (get(key) != null)
    return true;
   else
    return false;
  }

  @Override
  /** Return true if this map contains the value */
  public boolean containsValue(V value) {
   for (int i = 0; i < capacity; i++) {
    if (table[i] != null) {
     LinkedList<Entry<K, V>> bucket = table[i];
     for (Entry<K, V> entry : bucket)
      if (entry.getValue().equals(value))
       return true;
    }
   }

   return false;
  }

  @Override
  /** Return a set of entries in the map */
  public java.util.Set<MyMap.Entry<K, V>> entrySet() {
   java.util.Set<MyMap.Entry<K, V>> set = new java.util.HashSet<MyMap.Entry<K, V>>();

   for (int i = 0; i < capacity; i++) {
    if (table[i] != null) {
     LinkedList<Entry<K, V>> bucket = table[i];
     for (Entry<K, V> entry : bucket)
      set.add(entry);
    }
   }

   return set;
  }

  @Override
  /** Return the value that matches the specified key */
  public V get(K key) {
   int bucketIndex = hash(key.hashCode());
   if (table[bucketIndex] != null) {
    LinkedList<Entry<K, V>> bucket = table[bucketIndex];
    for (Entry<K, V> entry : bucket)
     if (entry.getKey().equals(key))
      return entry.getValue();
   }

   return null;
  }

  @Override
  /** Return true if this map contains no entries */
  public boolean isEmpty() {
   return size == 0;
  }

  @Override
  /** Return a set consisting of the keys in this map */
  public java.util.Set<K> keySet() {
   java.util.Set<K> set = new java.util.HashSet<K>();

   for (int i = 0; i < capacity; i++) {
    if (table[i] != null) {
     LinkedList<Entry<K, V>> bucket = table[i];
     for (Entry<K, V> entry : bucket)
      set.add(entry.getKey());
    }
   }

   return set;
  }

  @Override
  /** Add an entry (key, value) into the map */
  public V put(K key, V value) {
   if (get(key) != null) { // The key is already in the map
    int bucketIndex = hash(key.hashCode());
    LinkedList<Entry<K, V>> bucket = table[bucketIndex];
    for (Entry<K, V> entry : bucket)
     if (entry.getKey().equals(key)) {
      V oldValue = entry.getValue();
      // Replace old value with new value
      entry.value = value;
      // Return the old value for the key
      return oldValue;
     }
   }

   // Check load factor
   if (size >= capacity * loadFactorThreshold) {
    if (capacity == MAXIMUM_CAPACITY)
     throw new RuntimeException("Exceeding maximum capacity");

    rehash();
   }

   int bucketIndex = hash(key.hashCode());

   // Create a linked list for the bucket if it is not created
   if (table[bucketIndex] == null) {
    table[bucketIndex] = new LinkedList<Entry<K, V>>();
   }

   // Add a new entry (key, value) to hashTable[index]
   table[bucketIndex].add(new MyMap.Entry<K, V>(key, value));

   size++; // Increase size

   return value;
  }

  /** Remove the entries for the specified key */
  public void removeOne(K key) {
   int bucketIndex = hash(key.hashCode());

   // Remove the first entry that matches the key from a bucket
   if (table[bucketIndex] != null) {
    LinkedList<Entry<K, V>> bucket = table[bucketIndex];
    for (Entry<K, V> entry : bucket)
     if (entry.getKey().equals(key)) {
      bucket.remove(entry);
      size--; // Decrease size
      break; // Remove just one entry that matches the key
     }
   }
  }

  @Override
  /** Return the number of entries in this map */
  public int size() {
   return size;
  }

  @Override
  /** Return a set consisting of the values in this map */
  public java.util.Set<V> values() {
   java.util.Set<V> set = new java.util.HashSet<V>();

   for (int i = 0; i < capacity; i++) {
    if (table[i] != null) {
     LinkedList<Entry<K, V>> bucket = table[i];
     for (Entry<K, V> entry : bucket)
      set.add(entry.getValue());
    }
   }

   return set;
  }

  /** Hash function */
  private int hash(int hashCode) {
   return supplementalHash(hashCode) & (capacity - 1);
  }

  /** Ensure the hashing is evenly distributed */
  private static int supplementalHash(int h) {
   h ^= (h >>> 20) ^ (h >>> 12);
   return h ^ (h >>> 7) ^ (h >>> 4);
  }

  /** Return a power of 2 for initialCapacity */
  private int trimToPowerOf2(int initialCapacity) {
   int capacity = 1;
   while (capacity < initialCapacity) {
    capacity <<= 1;
   }

   return capacity;
  }

  /** Remove all entries from each bucket */
  private void removeEntries() {
   for (int i = 0; i < capacity; i++) {
    if (table[i] != null) {
     table[i].clear();
    }
   }
  }

  /** Rehash the map */
  @SuppressWarnings("unchecked")
  private void rehash() {
   java.util.Set<Entry<K, V>> set = entrySet(); // Get entries
   capacity <<= 1; // Double capacity
   table = new LinkedList[capacity]; // Create a new hash table
   size = 0; // Reset size to 0

   for (Entry<K, V> entry : set) {
    put(entry.getKey(), entry.getValue()); // Store to new table
   }
  }

  @Override
  public String toString() {
   StringBuilder builder = new StringBuilder("[");

   for (int i = 0; i < capacity; i++) {
    if (table[i] != null && table[i].size() > 0)
     for (Entry<K, V> entry : table[i])
      builder.append(entry);
   }

   builder.append("]");
   return builder.toString();
  }
 }

 interface MyMap<K, V> {
  /** Remove all of the entries from this map */
  public void clear();

  /** Return true if the specified key is in the map */
  public boolean containsKey(K key);

  /** Return true if this map contains the specified value */
  public boolean containsValue(V value);

  /** Return a set of entries in the map */
  public java.util.Set<Entry<K, V>> entrySet();

  /** Return the first value that matches the specified key */
  public V get(K key);

  /** Return true if this map contains no entries */
  public boolean isEmpty();

  /** Return a set consisting of the keys in this map */
  public java.util.Set<K> keySet();

  /** Add an entry (key, value) into the map */
  public V put(K key, V value);

  /** Remove the entries for the specified key */
  public void removeOne(K key);

  /** Return the number of mappings in this map */
  public int size();

  /** Return a set consisting of the values in this map */
  public java.util.Set<V> values();

  /** Define inner class for Entry */
  public static class Entry<K, V> {
   K key;
   V value;

   public Entry(K key, V value) {
    this.key = key;
    this.value = value;
   }

   public K getKey() {
    return key;
   }

   public V getValue() {
    return value;
   }

   @Override
   public String toString() {
    return "[" + key + ", " + value + "]";
   }
  }
 }

}

No comments :

Post a Comment