3 files changed, 33 insertions, 4 deletions

diff --git a/src/Simplex_tree/concept/SimplexTreeOptions.h b/src/Simplex_tree/concept/SimplexTreeOptions.h
index a50a2bf1..4a88f936 100644
--- a/src/Simplex_tree/concept/SimplexTreeOptions.h
+++ b/src/Simplex_tree/concept/SimplexTreeOptions.h
@@ -37,5 +37,7 @@ struct SimplexTreeOptions {
   static constexpr bool store_key;
   /// If true, each simplex has extra storage for one `Filtration_value`, and this value is propagated by operations like `Gudhi::Simplex_tree<SimplexTreeOptions>::expansion`. Without it, `Persistent_cohomology` degenerates to computing usual (non-persistent) cohomology.
   static constexpr bool store_filtration;
+  /// If true, the list of vertices present in the complex must always be 0, ..., num_vertices-1, without any hole.
+  static constexpr bool contiguous_vertices;
 };
 
diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree.h b/src/Simplex_tree/include/gudhi/Simplex_tree.h
index 4c6a95e8..74ae1713 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree.h
@@ -85,6 +85,7 @@ struct Simplex_tree_options_full_featured {
   typedef int Simplex_key;
   static const bool store_key = true;
   static const bool store_filtration = true;
+  static const bool contiguous_vertices = true;
 };
 
 /**
@@ -567,9 +568,22 @@ class Simplex_tree {
   /** \brief Returns the Simplex_handle corresponding to the 0-simplex
    * representing the vertex with Vertex_handle v. */
   Simplex_handle find_vertex(Vertex_handle v) {
-    return root_.members_.begin() + v;
+    if (Options::contiguous_vertices) {
+      assert(contiguous_vertices());
+      return root_.members_.begin() + v;
+    } else {
+      return root_.members_.find(v);
+    }
+  }
+
+ public:
+  /** \private \brief Test if the vertices have contiguous numbering: 0, 1, etc.  */
+  bool contiguous_vertices() const {
+    if(root_.members_.empty()) return true;
+    if(root_.members_.begin()->first!=0) return false;
+    if(std::prev(root_.members_.end())->first!=root_.members_.size()-1) return false;
+    return true;
   }
-  //{ return root_.members_.find(v); }
 
  private:
   /** \brief Inserts a simplex represented by a vector of vertex.
diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h b/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h
index 372ef329..f77bac15 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree/Simplex_tree_iterators.h
@@ -135,14 +135,27 @@ class Simplex_tree_boundary_simplex_iterator : public boost::iterator_facade<
     }
 
     Siblings * for_sib = sib_;
-    for (auto rit = suffix_.rbegin(); rit != suffix_.rend(); ++rit) {
+    Siblings * new_sib = sib_->oncles();
+    auto rit = suffix_.rbegin();
+    if (SimplexTree::Options::contiguous_vertices
+	&& new_sib == nullptr
+	&& rit != suffix_.rend()) {
+      // We reached the root, use a short-cut to find a vertex. We could also
+      // optimize finding the second vertex of a segment, but people are
+      // expected to call endpoints().
+      assert(st_->contiguous_vertices());
+      sh_ = for_sib->members_.begin()+*rit;
+      for_sib = sh_->second.children();
+      ++rit;
+    }
+    for (; rit != suffix_.rend(); ++rit) {
       sh_ = for_sib->find(*rit);
       for_sib = sh_->second.children();
     }
     sh_ = for_sib->find(last_);  // sh_ points to the right simplex now
     suffix_.push_back(next_);
     next_ = sib_->parent();
-    sib_ = sib_->oncles();
+    sib_ = new_sib;
   }
 
   // Most of the storage should be moved to the range, iterators should be light.