intersection.hxx
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3  * SHA - Simple Hybesis Algorithms
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5  * Copyright (c) Michael Jeulin-Lagarrigue
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20 #ifndef MODULE_COMBINATORY_INTERSECTION_HXX
21 #define MODULE_COMBINATORY_INTERSECTION_HXX
22 
23 // STD includes
24 #include <set>
25 
26 namespace SHA_Combinatory
27 {
41  template <typename Container, typename IT>
42  Container Intersection(const IT& beginFirst, const IT& endFirst,
43  const IT& beginSecond, const IT& endSecond)
44  {
45  // Take the smallest sequence for initial count
46  const auto kFirstSize = std::distance(beginFirst, endFirst);
47  const auto kSecondSize = std::distance(beginSecond, endSecond);
48  const bool kIsFirstSmaller = (kFirstSize <= kSecondSize);
49 
50  // Create and set enough capacity for the intersection
51  Container intersection;
52  intersection.reserve((kIsFirstSmaller) ? kFirstSize : kSecondSize);
53 
54  // Count each element of the smaller array
55  std::multiset<typename std::iterator_traits<IT>::value_type> count;
56  const auto kCountEndIt = (kIsFirstSmaller) ? endFirst : endSecond;
57  for (auto it = (kIsFirstSmaller) ? beginFirst : beginSecond; it != kCountEndIt; ++it)
58  count.insert(*it);
59 
60  // Push the element if find into the multiset and delete its instance from the counter
61  auto kIntersectEndIt = (kIsFirstSmaller) ? endSecond : endFirst;
62  for (auto it = (kIsFirstSmaller) ? beginSecond : beginFirst; it != kIntersectEndIt; ++it)
63  {
64  // Move element from count to intersection if found
65  auto foundIt = count.find(*it);
66  if (foundIt != count.end())
67  {
68  intersection.push_back(*it);
69  count.erase(foundIt);
70  }
71  }
72 
73  return intersection;
74  }
75 }
76 
77 #endif // MODULE_COMBINATORY_INTERSECTION_HXX
Container Intersection(const IT &beginFirst, const IT &endFirst, const IT &beginSecond, const IT &endSecond)