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diff --git a/extractor/precomputation.h b/extractor/precomputation.h
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+++ b/extractor/precomputation.h
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+#ifndef _PRECOMPUTATION_H_
+#define _PRECOMPUTATION_H_
+
+#include <memory>
+#include <unordered_map>
+#include <unordered_set>
+#include <tuple>
+#include <vector>
+
+#include <boost/filesystem.hpp>
+#include <boost/functional/hash.hpp>
+
+namespace fs = boost::filesystem;
+using namespace std;
+
+namespace extractor {
+
+typedef boost::hash<vector<int> > VectorHash;
+typedef unordered_map<vector<int>, vector<int>, VectorHash> Index;
+
+class SuffixArray;
+
+/**
+ * Data structure wrapping an index with all the occurrences of the most
+ * frequent discontiguous collocations in the source data.
+ *
+ * Let a, b, c be contiguous collocations. The index will contain an entry for
+ * every collocation of the form:
+ * - aXb, where a and b are frequent
+ * - aXbXc, where a and b are super-frequent and c is frequent or
+ *                b and c are super-frequent and a is frequent.
+ */
+class Precomputation {
+ public:
+  // Constructs the index using the suffix array.
+  Precomputation(
+      shared_ptr<SuffixArray> suffix_array, int num_frequent_patterns,
+      int num_super_frequent_patterns, int max_rule_span,
+      int max_rule_symbols, int min_gap_size,
+      int max_frequent_phrase_len, int min_frequency);
+
+  virtual ~Precomputation();
+
+  void WriteBinary(const fs::path& filepath) const;
+
+  // Returns a reference to the index.
+  virtual const Index& GetCollocations() const;
+
+  static int FIRST_NONTERMINAL;
+  static int SECOND_NONTERMINAL;
+
+ protected:
+  Precomputation();
+
+ private:
+  // Finds the most frequent contiguous collocations.
+  vector<vector<int> > FindMostFrequentPatterns(
+      shared_ptr<SuffixArray> suffix_array, const vector<int>& data,
+      int num_frequent_patterns, int max_frequent_phrase_len,
+      int min_frequency);
+
+  // Given the locations of the frequent contiguous collocations in a sentence,
+  // it adds new entries to the index for each discontiguous collocation
+  // matching the criteria specified in the class description.
+  void AddCollocations(
+      const vector<std::tuple<int, int, int> >& matchings, const vector<int>& data,
+      int max_rule_span, int min_gap_size, int max_rule_symbols);
+
+  // Adds an occurrence of a binary collocation.
+  void AddStartPositions(vector<int>& positions, int pos1, int pos2);
+
+  // Adds an occurrence of a ternary collocation.
+  void AddStartPositions(vector<int>& positions, int pos1, int pos2, int pos3);
+
+  Index collocations;
+};
+
+} // namespace extractor
+
+#endif