code: public static HashMap<Integer, Integer> readIntIntMap(Path path, FileSystem fs)
  	    throws IOException {
  		SequenceFile.Reader reader = new SequenceFile.Reader(fs, path, fs.getConf());
  
  		IntWritable topic = new IntWritable();
  		IntWritable value = new IntWritable();
  
  		HashMap<Integer, Integer> ret = new HashMap<Integer, Integer>();
  
  		while(reader.next(topic)) {
  			reader.getCurrentValue(value);
  
  			ret.put(topic.get(), value.get());
  		}
  
  		reader.close();
  		return ret;
  	}
docs: Reads maps of integer -> integer