content: /*
   * Copyright (C) 2011 Clearspring Technologies, Inc. 
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  /**
   *
   */
  package com.clearspring.analytics.stream;
  
  import java.util.List;
  import java.util.Random;
  
  /**
   * Estimates most frequently occurring items in a data stream
   * using a bounded amount of memory.
   * <p/>
   * Warning: this class is not thread safe.
   */
  public class StochasticTopper<T> implements ITopK<T> {
  
      private int sampleSize;
      private ISampleSet<T> sample;
      private Random random;
      private long count;
  
      public StochasticTopper(int sampleSize) {
          this(sampleSize, null);
      }
  
      public StochasticTopper(int sampleSize, Long seed) {
          this.sample = new SampleSet<T>(sampleSize);
          this.sampleSize = sampleSize;
  
          if (seed != null) {
              random = new Random(seed);
          } else {
              random = new Random();
          }
      }
  
      public boolean offer(T item, int incrementCount) {
          count++;
          boolean taken = false;
          if (sample.count() < sampleSize) {
              sample.put(item, incrementCount);
              taken = true;
          } else if (random.nextDouble() < sampleSize / (double) count) {
              sample.removeRandom();
              sample.put(item, incrementCount);
              taken = true;
          }
  
          return taken;
      }
  
      public boolean offer(T item) {
          return offer(item, 1);
      }
  
      /**
       * Retrieve top k items
       */
      public List<T> peek(int k) {
          return sample.peek(k);
      }
  }
  