summaryrefslogtreecommitdiff
path: root/src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Set_partition_iterator.h
diff options
context:
space:
mode:
Diffstat (limited to 'src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Set_partition_iterator.h')
-rw-r--r--src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Set_partition_iterator.h137
1 files changed, 137 insertions, 0 deletions
diff --git a/src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Set_partition_iterator.h b/src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Set_partition_iterator.h
new file mode 100644
index 00000000..46f67752
--- /dev/null
+++ b/src/Coxeter_triangulation/include/gudhi/Permutahedral_representation/Set_partition_iterator.h
@@ -0,0 +1,137 @@
+/* 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_SET_PARTITION_ITERATOR_H_
+#define PERMUTAHEDRAL_REPRESENTATION_SET_PARTITION_ITERATOR_H_
+
+#include <vector>
+#include <limits>
+#include <boost/range/iterator_range.hpp>
+
+namespace Gudhi {
+
+namespace coxeter_triangulation {
+
+typedef unsigned uint;
+
+/** \brief Class that allows the user to generate set partitions of a set {0,...,n-1} in k parts.
+ *
+*/
+class Set_partition_iterator : public boost::iterator_facade< Set_partition_iterator,
+ std::vector<std::vector<uint> > const,
+ boost::forward_traversal_tag> {
+ typedef std::vector<std::vector<uint> > value_t;
+
+protected:
+ friend class boost::iterator_core_access;
+
+ bool equal(Set_partition_iterator const& other) const {
+ return (is_end_ && other.is_end_);
+ }
+
+ value_t const& dereference() const {
+ return value_;
+ }
+
+ void update_value() {
+ for (uint i = 0; i < k_; i++)
+ value_[i].clear();
+ for (uint i = 0; i < n_; i++)
+ value_[rgs_[i]].push_back(i);
+ }
+
+ void increment() {
+ if (k_ <= 1) {
+ is_end_ = true;
+ return;
+ }
+ uint i = n_ - 1;
+ while (rgs_[i] + 1 > max_[i] ||
+ rgs_[i] + 1 >= k_)
+ i--;
+ if (i == 0) {
+ is_end_ = true;
+ return;
+ }
+ rgs_[i]++;
+ uint mm = max_[i];
+ mm += (rgs_[i] >= mm);
+ max_[i+1] = mm;
+ while (++i < n_) {
+ rgs_[i] = 0;
+ max_[i+1] = mm;
+ }
+ uint p = k_;
+ if (mm < p)
+ do {
+ max_[i] = p;
+ --i;
+ --p;
+ rgs_[i] = p;
+ } while (max_[i] < p);
+ update_value();
+ }
+
+public:
+
+ Set_partition_iterator(const uint& n, const uint& k)
+ :
+ value_(k),
+ rgs_(n, 0),
+ max_(n+1),
+ is_end_(n == 0),
+ n_(n),
+ k_(k)
+ {
+ max_[0] = std::numeric_limits<uint>::max();
+ for (uint i = 0; i <= n-k; ++i)
+ value_[0].push_back(i);
+ for (uint i = n-k+1, j = 1; i < n; ++i, ++j) {
+ rgs_[i] = j;
+ value_[j].push_back(i);
+ }
+ for (uint i = 1; i <= n; i++)
+ max_[i] = rgs_[i-1] + 1;
+ update_value();
+ }
+
+ // Used for creating an end iterator
+ Set_partition_iterator() : is_end_(true), n_(0), k_(0) {}
+
+ void reinitialize() {
+ if (n_ > 0)
+ is_end_ = false;
+ for (uint i = 0; i <= n_-k_; ++i)
+ rgs_[i] = 0;
+ for (uint i = n_-k_+1, j = 1; i < n_; ++i, ++j)
+ rgs_[i] = j;
+ for (uint i = 1; i <= n_; i++)
+ max_[i] = rgs_[i-1] + 1;
+ update_value();
+ }
+
+protected:
+ value_t value_; // the dereference value
+ std::vector<uint> rgs_; // restricted growth string
+ std::vector<uint> max_; // max_[i] = max(rgs_[0],...,rgs[i-1]) + 1
+ bool is_end_; // is true when the current permutation is the final one
+
+ uint n_;
+ uint k_;
+};
+
+} // namespace coxeter_triangulation
+
+} // namespace Gudhi
+
+
+#endif