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