Question

有任何方法可以使用STL在C ++中搜索项目或属性或变量我们可以使用任何提供Searching time as less as possible的STL容器。容器包含pair<int,int>。我想搜索一对p(a,x)，它应该返回p.first == Xi.first and p.second != Xi.second for all i的所有对X 例如
让容器是unordered_set。

  unordered_set< pair<int , int > > myset =
  {{1,2},{1,5},{1,6},{2,4},{3,5},{4,6},{6,7},{6,8}};
  if i search for p(1,5) then it should return pair(1,2),(1,6)
  if i search for p(2,4) or (3,5),(6,7) then it should return NULL i.e. nothing
  if i search for p(6,7) then it should return pair(6,8)

Answer 1

的内容

std::vector<std::pair<int, int>> 
  find_nonmatching_values(const std::unordered_multimap<int, int> & thing,
                          int key, int value) {
    std::vector<std::pair<int, int>> ret;
    auto range = thing.equal_range(key);
    std::copy_if(range.first, range.second, std::back_inserter(ret),
                 [value](const std::pair<const int, int> &p) 
                 { return p.second != value; });
    return ret;
}

Demo。对这段代码进行模板化是留给读者的练习。

Answer 2

比T.C.s版本更为通用：

#include <type_traits>
#include <iterator>

template <typename T, typename InputIterator, typename OutputIterator, typename Comparator>
void find_mismatches(InputIterator first, InputIterator last,
                     T const& val, OutputIterator out, Comparator comp)
{
    for (; first != last; ++first)
    {
        auto&& f = *first;
        if (!comp(f.second, val))
            *out++ = f;
    }
}

template <typename AssociativeCont, typename OutputIterator, typename Comparator>
void find_mismatches(AssociativeCont&& rng, typename std::remove_reference<AssociativeCont>::type::value_type const& val, OutputIterator out, Comparator comp)
{
    auto range = rng.equal_range(val.first);
    find_mismatches(range.first, range.second, val.second, out, comp);
}

template <typename AssociativeCont, typename OutputIterator>
void find_mismatches(AssociativeCont&& rng, typename std::remove_reference<AssociativeCont>::type::value_type const& val, OutputIterator out)
{
    auto range = rng.equal_range(val.first);
    find_mismatches(range.first, range.second, val.second, out, std::equal_to<decltype(val.second)>());
}

Demo。请注意，您仍然可以使用模板参数来扩展它，该模板参数是指向value_type成员的指针。

在c ++中使用STL搜索变量/ item / attribute？

2 个答案: