1 files changed, 80 insertions, 0 deletions
diff --git a/klm/util/multi_intersection.hh b/klm/util/multi_intersection.hh
new file mode 100644
index 00000000..8334d39d
--- /dev/null
+++ b/klm/util/multi_intersection.hh
@@ -0,0 +1,80 @@
+#ifndef UTIL_MULTI_INTERSECTION__
+#define UTIL_MULTI_INTERSECTION__
+
+#include <boost/optional.hpp>
+#include <boost/range/iterator_range.hpp>
+
+#include <algorithm>
+#include <functional>
+#include <vector>
+
+namespace util {
+
+namespace detail {
+template <class Range> struct RangeLessBySize : public std::binary_function<const Range &, const Range &, bool> {
+  bool operator()(const Range &left, const Range &right) const {
+    return left.size() < right.size();
+  }
+};
+
+/* Takes sets specified by their iterators and a boost::optional containing
+ * the lowest intersection if any.  Each set must be sorted in increasing
+ * order.  sets is changed to truncate the beginning of each sequence to the
+ * location of the match or an empty set.  Precondition: sets is not empty
+ * since the intersection over null is the universe and this function does not
+ * know the universe.   
+ */
+template <class Iterator, class Less> boost::optional<typename std::iterator_traits<Iterator>::value_type> FirstIntersectionSorted(std::vector<boost::iterator_range<Iterator> > &sets, const Less &less = std::less<typename std::iterator_traits<Iterator>::value_type>()) {
+  typedef std::vector<boost::iterator_range<Iterator> > Sets;
+  typedef typename std::iterator_traits<Iterator>::value_type Value;
+
+  assert(!sets.empty());
+
+  if (sets.front().empty()) return boost::optional<Value>();
+  // Possibly suboptimal to copy for general Value; makes unsigned int go slightly faster.  
+  Value highest(sets.front().front());
+  for (typename Sets::iterator i(sets.begin()); i != sets.end(); ) {
+    i->advance_begin(std::lower_bound(i->begin(), i->end(), highest, less) - i->begin());
+    if (i->empty()) return boost::optional<Value>();
+    if (less(highest, i->front())) {
+      highest = i->front();
+      // start over
+      i = sets.begin();
+    } else {
+      ++i;
+    }
+  }
+  return boost::optional<Value>(highest);
+}
+
+} // namespace detail
+
+template <class Iterator, class Less> boost::optional<typename std::iterator_traits<Iterator>::value_type> FirstIntersection(std::vector<boost::iterator_range<Iterator> > &sets, const Less less) {
+  assert(!sets.empty());
+
+  std::sort(sets.begin(), sets.end(), detail::RangeLessBySize<boost::iterator_range<Iterator> >());
+  return detail::FirstIntersectionSorted(sets, less);
+}
+
+template <class Iterator> boost::optional<typename std::iterator_traits<Iterator>::value_type> FirstIntersection(std::vector<boost::iterator_range<Iterator> > &sets) {
+  return FirstIntersection(sets, std::less<typename std::iterator_traits<Iterator>::value_type>());
+}
+
+template <class Iterator, class Output, class Less> void AllIntersection(std::vector<boost::iterator_range<Iterator> > &sets, Output &out, const Less less) {
+  typedef typename std::iterator_traits<Iterator>::value_type Value;
+  assert(!sets.empty());
+
+  std::sort(sets.begin(), sets.end(), detail::RangeLessBySize<boost::iterator_range<Iterator> >());
+  boost::optional<Value> ret;
+  for (boost::optional<Value> ret; ret = detail::FirstIntersectionSorted(sets, less); sets.front().advance_begin(1)) {
+    out(*ret);
+  }
+}
+
+template <class Iterator, class Output> void AllIntersection(std::vector<boost::iterator_range<Iterator> > &sets, Output &out) {
+  AllIntersection(sets, out, std::less<typename std::iterator_traits<Iterator>::value_type>());
+}
+
+} // namespace util
+
+#endif // UTIL_MULTI_INTERSECTION__