solved s09 ex4

09/src/main/java/ch/zhaw/ads/MyHashtable.java

@@ -1,3 +1,5 @@
+package ch.zhaw.ads;
+
 import java.util.*;
 
 public class MyHashtable<K,V> implements java.util.Map<K,V> {
@@ -5,48 +7,87 @@ public class MyHashtable<K,V> implements java.util.Map<K,V> {
     private V[] values = (V[]) new Object[10];
 
     private int hash(Object k) {
-        int h = Math.abs(k.hashCode());
-        return h % keys.length;
+        int h = Math.abs(k.hashCode()) % keys.length;
+        int counter = 0;
+
+        while (keys[h] != null && !keys[h].equals(k)) {
+            h = (h + 1) % keys.length;
+            counter++;
+            if (counter >= keys.length) return -1;
+        }
+        return h;
     }
 
     public MyHashtable(int size) {
-        // to be done
+        keys =   (K[]) new Object[size];
+        values = (V[]) new Object[size];
     }
 
     //  Removes all mappings from this map (optional operation).
     public void clear() {
-        // to be done
-        throw new UnsupportedOperationException();
+        keys =   (K[]) new Object[keys.length];
+        values = (V[]) new Object[values.length];
     }
 
     //  Associates the specified value with the specified key in this map (optional operation).
     public V put(K key, V value) {
-        // to be done
-        throw new UnsupportedOperationException();
+        if (size() >= keys.length) {
+            keys = Arrays.copyOf(keys, keys.length * 2);
+            values = Arrays.copyOf(values, values.length * 2);
+            rehash();
+        }
+
+        int keyId = hash(key);
+        if (keyId < 0) return null;
+
+        values[keyId] = value;
+        keys[keyId] = key;
+
+        return value;
     }
 
     //  Returns the value to which this map maps the specified key.
     public V get(Object key) {
-        // to be done
-        throw new UnsupportedOperationException();
+        if (key == null) return null;
+        return values[hash((K) key)];
     }
 
     //  Returns true if this map contains no key-value mappings.
     public boolean isEmpty() {
-        // to be done
-        throw new UnsupportedOperationException();
+        return size() == 0;
     }
 
     //  Removes the mapping for this key from this map if present (optional operation).
     public V remove(Object key) {
-        // to be done (Aufgabe 3)
-        throw new UnsupportedOperationException();
+        int keyId = hash((K) key);
+        if (keyId < 0) return null;
+
+        V removed = values[keyId];
+        values[keyId] = null;
+        keys[keyId] = null;
+        rehash();
+        return removed;
     }
 
     //  Returns the number of key-value mappings in this map.
     public int size() {
-        // to be done
-        throw new UnsupportedOperationException();
+        int size = 0;
+        for (int i = 0; i < keys.length; i++) {
+            if (keys[i] != null) size++;
+        }
+        return size;
+    }
+
+    private void rehash() {
+        K[] keysClone = keys.clone();
+        V[] valuesClone = values.clone();
+        clear();
+
+        for (int i = 0; i < keys.length; i++) {
+            if (keysClone[i] != null) {
+                put(keysClone[i], valuesClone[i]);
+            }
+        }
     }
 
     // =======================================================================

09/src/test/java/ch/zhaw/ads/HashTest.java

@@ -1,3 +1,5 @@
+package ch.zhaw.ads;
+
 import org.junit.Test;
 import org.junit.Before;
 import static org.junit.Assert.*;