1 files changed, 130 insertions, 0 deletions
diff --git a/src/de/fhswf/in/inf/java1/aufgabe8/FloydAndBentley.java b/src/de/fhswf/in/inf/java1/aufgabe8/FloydAndBentley.java
new file mode 100644
index 0000000..54dd863
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+++ b/src/de/fhswf/in/inf/java1/aufgabe8/FloydAndBentley.java
@@ -0,0 +1,130 @@
+/**
+ * 
+ */
+package de.fhswf.in.inf.java1.aufgabe8;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+
+/**
+ * Utility class for the Floyd and Bentley algorithm.
+ *
+ * @author $Author: $
+ * @version $Revision: $, $Date: $ UTC
+ */
+public final class FloydAndBentley
+{
+
+   private static Random rnd = new Random();
+
+   /**
+    * Private constructor for utility class.
+    *
+    */
+   private FloydAndBentley()
+   {
+   }
+
+   /**
+    * A function which chooses a sample from a List with the Floyd and Bentley
+    * algorithm. (Recursive algorithm)
+    *
+    * @param <T>
+    *           Type of the Lists.
+    * @param s
+    *           The set from which the sample is chosen.
+    * @param k
+    *           The number of items to be chosen.
+    * @return Return the sample.
+    */
+   public static <T> List<T> sample(List<T> s, int k)
+   {
+      if (s.isEmpty())
+      {
+         throw new IllegalArgumentException("Set is empty");
+      }
+      if (k > s.size())
+      {
+         throw new IllegalArgumentException("k is bigger than the Set");
+      }
+
+      List<T> ret = new ArrayList<>(k);
+      sampleRec(s, k, ret);
+
+      return ret;
+
+   }
+
+   /**
+    * The recursive implementation of the Floyd and Bentley algorithm.
+    *
+    * @param <T>
+    *           Type of the Lists.
+    * @param s
+    *           The set from which the sample is chosen.
+    * @param k
+    *           The number of items to be chosen.
+    * @param ret
+    *           Return the sample.
+    */
+   private static <T> void sampleRec(List<T> s, int k, List<T> ret)
+   {
+      if (ret.size() >= k)
+      {
+         return;
+      }
+
+      T val = s.get(rnd.nextInt(s.size() - (k - ret.size())));
+
+      if (ret.contains(val))
+      {
+         val = s.get(s.size() - (k - ret.size()));
+      }
+
+      ret.add(val);
+
+      sampleRec(s, k, ret);
+
+   }
+
+   /**
+    * A function which chooses a sample from a List with the Floyd and Bentley
+    * algorithm. (Non recursive algorithm)
+    *
+    * @param <T>
+    *           Type of the Lists.
+    * @param s
+    *           The set from which the sample is chosen.
+    * @param k
+    *           The number of items to be chosen.
+    * @return Return the sample.
+    */
+   public static <T> List<T> sample2(List<T> s, int k)
+   {
+      if (s.isEmpty())
+      {
+         throw new IllegalArgumentException("Set is empty");
+      }
+      if (k > s.size())
+      {
+         throw new IllegalArgumentException("k is bigger than the Set");
+      }
+
+      List<T> ret = new ArrayList<>(k);
+
+      for (int i = 0; i < k; i++)
+      {
+         T val = s.get(rnd.nextInt(s.size() - (k - ret.size())));
+
+         if (ret.contains(val))
+         {
+            val = s.get(s.size() - (k - ret.size()));
+         }
+
+         ret.add(val);
+      }
+
+      return ret;
+   }
+}