1 files changed, 101 insertions, 0 deletions
diff --git a/src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Combination_iterator.h b/src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Combination_iterator.h
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+++ b/src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Combination_iterator.h
@@ -0,0 +1,101 @@
+/*    This file is part of the Gudhi Library. The Gudhi library
+ *    (Geometric Understanding in Higher Dimensions) is a generic C++
+ *    library for computational topology.
+ *
+ *    Author(s):       Siargey Kachanovich
+ *
+ *    Copyright (C) 2019 Inria
+ *
+ *    Modification(s):
+ *      - YYYY/MM Author: Description of the modification
+ */
+
+#ifndef PERMUTAHEDRAL_REPRESENTATION_COMBINATION_ITERATOR_H_
+#define PERMUTAHEDRAL_REPRESENTATION_COMBINATION_ITERATOR_H_
+
+#include <vector>
+#include <boost/range/iterator_range.hpp>
+
+namespace Gudhi {
+
+namespace coxeter_triangulation {
+
+typedef unsigned uint;
+
+/** \brief Class that allows the user to generate combinations of 
+ *   k elements in a set of n elements.
+ *  Based on the algorithm by Mifsud.
+*/
+class Combination_iterator : public boost::iterator_facade< Combination_iterator,
+							    std::vector<uint> const,
+							    boost::forward_traversal_tag> {
+  typedef std::vector<uint> value_t;
+  
+protected:
+  friend class boost::iterator_core_access;
+  
+  bool equal(Combination_iterator const& other) const {
+    return (is_end_ && other.is_end_);
+  }
+
+  value_t const& dereference() const {
+    return value_;
+  }
+
+  void increment() {
+    if (value_[0] == n_ - k_) {
+      is_end_ = true;
+      return;
+    }
+    uint j = k_ - 1;
+    if (value_[j] < n_ - 1) {
+      value_[j]++;
+      return;
+    }
+    for (; j > 0; --j)
+      if (value_[j-1] < n_ - k_ + j-1) {
+	value_[j-1]++;
+	for (uint s = j; s < k_; s++)
+	  value_[s] = value_[j-1] + s - (j-1);
+	return;
+      }
+  }
+
+public:
+  
+  Combination_iterator(const uint& n, const uint& k)
+    :
+    value_(k),
+    is_end_(n == 0),
+    n_(n),
+    k_(k)
+  {
+    for (uint i = 0; i < k; ++i)
+      value_[i] = i;
+  }
+
+  // Used for the creating an end iterator
+  Combination_iterator() : is_end_(true), n_(0), k_(0) {}
+
+  void reinitialize() {
+    if (n_ > 0) {
+      is_end_ = false;
+      for (uint i = 0; i < n_; ++i)
+      value_[i] = i;
+    }
+  }
+  
+protected:
+  value_t value_; // the dereference value
+  bool is_end_;   // is true when the current permutation is the final one 
+
+  uint n_;
+  uint k_;
+};
+
+} // namespace coxeter_triangulation
+
+} // namespace Gudhi
+
+
+#endif