std::ranges::includes(3)

NAME
std::ranges::includes - std::ranges::includes

Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::input_iterator I1, std::sentinel_for<I1> S1,
   std::input_iterator I2, std::sentinel_for<I2> S2,
   class Proj1 = std::identity, class Proj2 = std::identity,
   std::indirect_strict_weak_order< (1) (since C++20)
   std::projected<I1, Proj1>,
   std::projected<I2, Proj2>> Comp = ranges::less >
   constexpr bool includes( I1 first1, S1 last1, I2 first2, S2 last2,
   Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {} )
   template< ranges::input_range R1, ranges::input_range R2,
   class Proj1 = std::identity, class Proj2 = std::identity,
   std::indirect_strict_weak_order<
   std::projected<ranges::iterator_t<R1>, Proj1>, (2) (since C++20)
   std::projected<ranges::iterator_t<R2>, Proj2>> Comp = ranges::less
   >
   constexpr bool includes( R1&& r1, R2&& r2, Comp comp = {},
   Proj1 proj1 = {}, Proj2 proj2 = {} )
   1) Returns true if the projections of the sorted range [first2, last2) is a
   subsequence of the projections of the sorted range [first1, last1).
   2) Same as (1), but uses r1 and r2 as the source ranges, as if by using
   ranges::begin(r1) and ranges::begin(r2) as first1 and first2 respectively, and
   ranges::end(r1) and ranges::end(r2) as last1 and last2 respectively.
   Both ranges must be sorted with the given comparison function comp. A subsequence
   need not be contiguous.
   The function-like entities described on this page are niebloids, that is:
     * Explicit template argument lists may not be specified when calling any of them.
     * None of them is visible to argument-dependent lookup.
     * When one of them is found by normal unqualified lookup for the name to the left
       of the function-call operator, it inhibits argument-dependent lookup.
   In practice, they may be implemented as function objects, or with special compiler
   extensions.

Parameters
   first1, last1 - the sorted range of elements to examine
   r1 - the sorted range of elements to examine
   first2, last2 - the sorted range of elements to search for
   r2 - the sorted range of elements to search for
   comp - comparison function to apply to the projected elements
   proj1 - projection to apply to the elements in the first range
   proj2 - projection to apply to the elements in the second range

Return value
   true if [first2, last2) is a subsequence of [first1, last1); otherwise false.

Complexity
   At most \(\scriptsize 2 \cdot (N_1+N_2-1)\)2·(N[1]+N[2]-1) comparisons, where
   \(\scriptsize N_1\)N[1] is ranges::distance(r1) and \(\scriptsize N_2\)N[2] is
   ranges::distance(r2).

Possible implementation
   struct includes_fn {
     template<std::input_iterator I1, std::sentinel_for<I1> S1,
              std::input_iterator I2, std::sentinel_for<I2> S2,
              class Proj1 = std::identity, class Proj2 = std::identity,
              std::indirect_strict_weak_order<
                  std::projected<I1, Proj1>,
                  std::projected<I2, Proj2>> Comp = ranges::less>
     constexpr bool operator()(I1 first1, S1 last1, I2 first2, S2 last2,
                        Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
     {
         for (; first2 != last2; ++first1)
         {
             if (first1 == last1 && comp(*first2, *first1))
                 return false;
             if (!comp(*first1, *first2))
                 ++first2;
         }
         return true;
     }
     template<ranges::input_range R1, ranges::input_range R2,
              class Proj1 = std::identity, class Proj2 = std::identity,
              std::indirect_strict_weak_order<
                  std::projected<ranges::iterator_t<R1>, Proj1>,
                  std::projected<ranges::iterator_t<R2>, Proj2>> Comp = ranges::less>
     constexpr bool operator()(R1&& r1, R2&& r2, Comp comp = {},
                        Proj1 proj1 = {}, Proj2 proj2 = {}) const
     {
       return (*this)(ranges::begin(r1), ranges::end(r1),
                      ranges::begin(r2), ranges::end(r2),
                      std::ref(comp), std::ref(proj1), std::ref(proj2));
     }
   };
   inline constexpr auto includes = includes_fn{};

Example
// Run this code
 #include <algorithm>
 #include <cctype>
 #include <initializer_list>
 #include <iomanip>
 #include <iostream>
 #include <locale>
 #include <string>
 template <class T>
 std::ostream& operator<<(std::ostream& os, std::initializer_list<T> const& list)
 {
     for (os << "{ "; auto const& elem : list)
         os << elem << ' ';
     return os << "} ";
 }
 struct true_false : std::numpunct<char>
 {
     std::string do_truename() const { return "? Yes\n"; }
     std::string do_falsename() const { return "? No\n"; }
 };
 int main()
 {
     std::cout.imbue(std::locale(std::cout.getloc(), new true_false));
     auto ignore_case = [](char a, char b) { return std::tolower(a) < std::tolower(b); };
     const auto
         a = {'a', 'b', 'c'},
         b = {'a', 'c'},
         c = {'a', 'a', 'b'},
         d = {'g'},
         e = {'a', 'c', 'g'},
         f = {'A', 'B', 'C'},
         z = {'a', 'b', 'c', 'f', 'h', 'x'};
     std::cout
         << z << "includes\n" << std::boolalpha
         << a << std::ranges::includes(z.begin(), z.end(), a.begin(), a.end())
         << b << std::ranges::includes(z, b)
         << c << std::ranges::includes(z, c)
         << d << std::ranges::includes(z, d)
         << e << std::ranges::includes(z, e)
         << f << std::ranges::includes(z, f, ignore_case);
 }

Output:
 { a b c f h x } includes
 { a b c } ? Yes
 { a c } ? Yes
 { a a b } ? No
 { g } ? No
 { a c g } ? No
 { A B C } ? Yes

See also
   ranges::set_difference computes the difference between two sets
   (C++20) (niebloid)
   ranges::search searches for a range of elements
   (C++20) (niebloid)
   includes returns true if one sequence is a subsequence of another
                        (function template)