// Copyright 2013, University of Freiburg,
// Chair of Algorithms and Data Structures.
// Author: Hannah Bast <bast@cs.uni-freiburg.de>.

// NOTE: this is a code design suggestion in pseudo-code. It is not supposed to
// be compilable in any language. You have to translate it to Java or C++
// yourself. The purpose of this file is to suggest a basic design and settle
// questions you might have on what exactly your code is supossed to do.

// Implementation of a very simple inverted index.
class InvertedIndex {
  // PUBLIC MEMBERS

  // Create an empty index.
  InvertedIndex();

  // Build inverted lists from a given text file. The expected format of the
  // file is one line per document with each line containing the text from the
  // document without newlines.
  //
  // IMPLEMENTATION NOTE: convert all words to lower case. If a word occurs
  // multiple times in a document, add the document id only once to the inverted
  // list.
  void buildFromTextFile(String fileName);

  // Given a query, return a list of all documents, sorted by document id, that
  // contain all of the words in the query. If there are more than k such
  // documents, return only the first k in that order, for the given value of k.
  //
  // IMPLEMENTATION NOTE: do iterative pair-wise intersection, as explained in
  // the lecture, and using method intersect below.
  Array<String> processQuery(String query, int k);

  // PRIVATE MEMBERS

  // Intersect two sorted lists of integers. Returns the result list = sorted
  // list of ids contained in both input lists.
  //
  // IMPLEMENTATION NOTE: use the simple linear-time intersect explained in the
  // lecture.
  Array<int> intersect(Array<int> list1, Array<int> list2);

  // The inverted lists = a sorted list of document ids, one for each word that
  // occurs at least once in the given collection.
  Map<String, Array<int>> invertedLists;

  // The text of all the documents, indexed by document id. Since document ids
  // are consecutive, starting at 0, a simple array suffices.
  Array<String> documents;
}