HashTableMap original

map/HashTableMap.java

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+package map;
+
+
+import position.NodePositionList;
+import position.PositionList;
+import priorityqueue.Entry;
+
+import java.security.InvalidKeyException;
+
+/**
+  * A hash table data structure that uses linear probing to handle
+  * collisions. The hash function uses the built-in hashCode method
+  * and the multiply-add-and-divide method.  The load factor is alwyas
+  * kept less than or equal to 0.5. When the load factor reaches 0.5,
+  * the entries are rehashed into a new bucket array with twice the
+  * capacity.
+  *
+  * @author Roberto Tamassia, Michael Goodrich, Eric Zamore
+  */
+
+public class HashTableMap<K,V> implements Map<K,V> {
+
+  public static class HashEntry<K,V> implements Entry<K,V> {
+    protected K key;
+    protected V value;
+    public HashEntry(K k, V v) { key = k; value = v; }
+    public V getValue() { return value; }
+    public K getKey() { return key; }
+    public V setValue(V val) {
+      V oldValue = value;
+      value = val;
+      return oldValue;
+      }
+    public boolean equals(Object o) {
+      HashEntry<K,V> ent;
+      try { ent = (HashEntry<K,V>) o; }
+      catch (ClassCastException ex) { return false; }
+      return (ent.getKey() == key) && (ent.getValue() == value);
+    }
+
+    public String toString() {
+      return "(" + key + "," + value + ")";
+    }
+
+  }
+  protected Entry<K,V> AVAILABLE = new HashEntry<K,V>(null, null);
+  protected int n = 0; 		// number of entries in the dictionary
+  protected int prime, capacity; // prime factor and capacity of bucket array
+  protected Entry<K,V>[] bucket;// bucket array
+  protected long scale, shift;   // the shift and scaling factors
+
+  /** Creates a hash table with prime factor 109345121 and capacity 1000. */
+  public HashTableMap() { this(109345121,1000); }
+
+  /** Creates a hash table with prime factor 109345121 and given capacity. */
+  public HashTableMap(int cap) { this(109345121, cap); }
+
+  /** Creates a hash table with the given prime factor and capacity. */
+  public HashTableMap(int p, int cap) {
+    prime = p;
+    capacity = cap;
+    bucket = (Entry<K,V>[]) new Entry[capacity]; // safe cast
+    java.util.Random rand = new java.util.Random();
+    scale = rand.nextInt(prime-1) + 1;
+    shift = rand.nextInt(prime);
+  }
+
+  /** Determines whether a key is valid. */
+  protected void checkKey(K k) throws InvalidKeyException{
+    if (k == null) throw new InvalidKeyException("Invalid key: null.");
+  }
+
+  /** Hash function applying MAD method to default hash code. */
+  public int hashValue(K key) {
+    return (int) ((Math.abs(key.hashCode()*scale + shift) % prime) % capacity);
+  }
+
+  /** Returns the number of entries in the hash table. */
+  public int size() { return n; }
+
+  /** Returns whether or not the table is empty. */
+  public boolean isEmpty() { return (n == 0); }
+
+  /** Returns an iterable object containing all of the keys. */
+  public Iterable<K> keys() {
+    PositionList<K> keys = new NodePositionList<K>();
+    for (int i=0; i<capacity; i++) 
+      if ((bucket[i] != null) && (bucket[i] != AVAILABLE)) 
+	keys.addLast(bucket[i].getKey());
+    return keys;
+  }
+
+  /** Helper search method - returns index of found key or -(a + 1),
+   * where a is the index of the first empty or available slot found. */
+  protected int findEntry(K key) throws InvalidKeyException {
+    int avail = -1;
+    checkKey(key);
+    int i = hashValue(key);
+    int j = i;
+    do {
+      Entry<K,V> e = bucket[i];
+      if ( e == null) {
+	    if (avail < 0)
+	        avail = i;	// key is not in table
+	    break;
+      }
+      if (key.equals(e.getKey())) // we have found our key
+	    return i;	// key found
+      if (e == AVAILABLE) {	// bucket is deactivated
+	    if (avail < 0)
+	        avail = i;	// remember that this slot is available
+      }
+      i = (i + 1) % capacity;	// keep looking
+    } while (i != j);
+    return -(avail + 1);  // first empty or available slot
+  }
+
+  /** Returns the value associated with a key. */
+  public V get (K key) throws InvalidKeyException {
+    int i = findEntry(key);  // helper method for finding a key
+    if (i < 0) return null;  // there is no value for this key, so reutrn null
+    return bucket[i].getValue();     // return the found value in this case
+  }
+
+  /** Put a key-value pair in the map, replacing previous one if it exists. */
+  public V put (K key, V value) throws InvalidKeyException {
+    int i = findEntry(key); //find the appropriate spot for this entry
+    if (i >= 0)	//  this key has a previous value
+      return ((HashEntry<K,V>) bucket[i]).setValue(value); // set new value 
+    if (n >= capacity/2) {
+      rehash(); // rehash to keep the load factor <= 0.5
+      i = findEntry(key); //find again the appropriate spot for this entry
+    }
+    bucket[-i-1] = new HashEntry<K,V>(key, value); // convert to proper index
+    n++;
+    return null; 	// there was no previous value
+  }
+
+  /** Doubles the size of the hash table and rehashes all the entries. */
+  protected void rehash() throws InvalidKeyException{
+    capacity = 2*capacity;
+    Entry<K,V>[] old = bucket;
+    bucket = (Entry<K,V>[]) new Entry[capacity]; // new bucket is twice as big 
+    java.util.Random rand = new java.util.Random();
+    scale = rand.nextInt(prime-1) + 1;    	// new hash scaling factor
+    shift = rand.nextInt(prime); 		// new hash shifting factor
+    for (int i=0; i<old.length; i++) {
+      Entry<K,V> e = old[i];
+      if ((e != null) && (e != AVAILABLE)) { // a valid entry
+	    int j = - 1 - findEntry(e.getKey());
+	    bucket[j] = e;
+      }
+    }
+  }
+
+  /** Removes the key-value pair with a specified key. */
+  public V remove (K key) throws InvalidKeyException {
+    int i = findEntry(key);  	// find this key first
+    if (i < 0) return null;  	// nothing to remove
+    V toReturn = bucket[i].getValue();
+    bucket[i] = AVAILABLE; 		// mark this slot as deactivated
+    n--;
+    return toReturn;
+  }
+
+  /** Returns an iterable object containing all of the entries. */
+  public Iterable<Entry<K,V>> entries() {
+    PositionList<Entry<K,V>> entries = new NodePositionList<Entry<K,V>>();
+    for (int i=0; i<capacity; i++) 
+      if ((bucket[i] != null) && (bucket[i] != AVAILABLE)) 
+	entries.addLast(bucket[i]);
+    return entries;
+  }
+
+  /** Returns an iterable object containing all of the values. */
+  public Iterable<V> values() {
+    PositionList<V> values = new NodePositionList<V>();
+    for (int i=0; i<capacity; i++) 
+      if ((bucket[i] != null) && (bucket[i] != AVAILABLE)) 
+	values.addLast(bucket[i].getValue());
+    return values;
+  }
+
+} 
+