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std::ranges::find_end(3)       C++ Standard Libary	std::ranges::find_end(3)

NAME
     std::ranges::find_end - std::ranges::find_end

Synopsis
	Defined in header <algorithm>
	Call signature
	template< std::forward_iterator I1, std::sentinel_for<I1> S1,

		  std::forward_iterator I2, std::sentinel_for<I2> S2,
		  class Pred = ranges::equal_to,
		  class 	    Proj1	     =		  std::identity,
     (since
		  class Proj2 = std::identity > 			     (1)
     C++20)
	requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
	constexpr ranges::subrange<I1>
	    find_end( I1 first1, S1 last1, I2 first2, S2 last2,

		      Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );
	template< ranges::forward_range R1, ranges::forward_range R2,

		  class Pred = ranges::equal_to,
		  class Proj1 = std::identity,
		  class Proj2 = std::identity >
	requires  std::indirectly_comparable<ranges::iterator_t<R1>,	     (2)
     (since
					    ranges::iterator_t<R2>,
     C++20)
					    Pred, Proj1, Proj2>
	constexpr ranges::borrowed_subrange_t<R1>
	    find_end( R1&& r1, R2&& r2, Pred pred = {},

		      Proj1 proj1 = {}, Proj2 proj2 = {} );

	1) Searches for the last occurrence of the sequence [first2,  last2)  in
     the range
	[first1, last1), after projection with proj1 and proj2 respectively. The
     projected
	elements are compared using the binary predicate pred.
	2) Same as (1), but uses r1 as the first source range and r2 as the sec-
     ond source
	range,	as  if	using  ranges::begin(r1)  as  first1, ranges::end(r1) as
     last1,
	ranges::begin(r2) as first2, and ranges::end(r2) as last2.

	The function-like entities described on this page  are	niebloids,  that
     is:

	  *  Explicit  template  argument lists cannot be specified when calling
     any of them.
	  * None of them are visible to argument-dependent lookup.
	  * When any of them are found by normal unqualified lookup as the  name
     to the left
	    of	the  function-call operator, argument-dependent lookup is inhib-
     ited.

	In practice, they may be implemented as function objects, or  with  spe-
     cial compiler
	extensions.

Parameters
	first1, last1 - the range of elements to examine (aka haystack)
	first2, last2 - the range of elements to search for (aka needle)
	r1	      - the range of elements to examine (aka haystack)
	r2	      - the range of elements to search for (aka needle)
	pred	      - binary predicate to compare the 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
	1)  ranges::subrange<I1>{}  value initialized with expression {i, i + (i
     == last1 ? 0
	: ranges::distance(first2, last2))} that denotes the last occurrence  of
     the sequence
	[first2,  last2)  in range [first1, last1) (after projections with proj1
     and proj2).
	If [first2, last2) is empty or if no such sequence is found, the  return
     value is
	effectively initialized with {last1, last1}.
	2)  Same  as  (1),  except that the return type is ranges::borrowed_sub-
     range_t<R1>.

Complexity
	At most \(\scriptsize S\cdot(N-S+1)\)SA.(N-S+1) applications of the cor-
     responding
	predicate and each projection, where \(\scriptsize S\)S is  ranges::dis-
     tance(first2,
	last2)	and  \(\scriptsize  N\)N  is ranges::distance(first1, last1) for
     (1), or
	\(\scriptsize S\)S is ranges::distance(r2) and \(\scriptsize N\)N is
	ranges::distance(r1) for (2).

Notes
	An implementation can improve efficiency of the search if the input  it-
     erators model
	std::bidirectional_iterator by searching from the end towards the begin.
     Modelling
	the  std::random_access_iterator  may  improve the comparison speed. All
     this however
	does not change the theoretical complexity of the worst case.

Possible implementation
	struct find_end_fn
	{
	    template<std::forward_iterator I1, std::sentinel_for<I1> S1,
		     std::forward_iterator I2, std::sentinel_for<I2> S2,
		     class Pred = ranges::equal_to,
		     class Proj1 = std::identity, class Proj2 = std::identity>
	    requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
	    constexpr ranges::subrange<I1>
		operator()(I1 first1, S1 last1,
			   I2 first2, S2 last2, Pred pred = {},
			   Proj1 proj1 = {}, Proj2 proj2 = {}) const
	    {
		if (first2 == last2)
		{
		    auto last_it = ranges::next(first1, last1);
		    return {last_it, last_it};
		}
		auto result = ranges::search(
		    std::move(first1),	last1,	first2,  last2,   pred,   proj1,
     proj2);

		if (result.empty())
		    return result;

		for (;;)
		{
		    auto new_result = ranges::search(
			std::next(result.begin()),  last1,  first2, last2, pred,
     proj1, proj2);
		    if (new_result.empty())
			return result;
		    else
			result = std::move(new_result);
		}
	    }

	    template<ranges::forward_range R1, ranges::forward_range R2,
		     class Pred = ranges::equal_to,
		     class Proj1 = std::identity,
		     class Proj2 = std::identity>
	    requires std::indirectly_comparable<ranges::iterator_t<R1>,
						ranges::iterator_t<R2>,
						Pred, Proj1, Proj2>
	    constexpr ranges::borrowed_subrange_t<R1>
		operator()(R1&& r1, R2&& r2, Pred pred = {},
			   Proj1 proj1 = {}, Proj2 proj2 = {}) const
	    {
		return (*this)(ranges::begin(r1), ranges::end(r1),
			       ranges::begin(r2), ranges::end(r2),
			       std::move(pred),
			       std::move(proj1), std::move(proj2));
	    }
	};

	inline constexpr find_end_fn find_end {};

Example
     // Run this code

      #include <algorithm>
      #include <array>
      #include <cctype>
      #include <iostream>
      #include <ranges>
      #include <string_view>

      void print(const auto haystack, const auto needle)
      {
	  const auto pos = std::distance(haystack.begin(), needle.begin());
	  std::cout << "In \"";
	  for (const auto c : haystack)
	      std::cout << c;
	  std::cout << "\" found \"";
	  for (const auto c : needle)
	      std::cout << c;
	  std::cout << "\" at position [" << pos << ".." << pos +  needle.size()
     << ")\n"
	      << std::string(4 + pos, ' ') << std::string(needle.size(), '^') <<
     '\n';
      }

      int main()
      {
	  using namespace std::literals;
	  constexpr auto secret{"password password word..."sv};
	  constexpr auto wanted{"password"sv};

	  constexpr auto found1 = std::ranges::find_end(
	      secret.cbegin(), secret.cend(), wanted.cbegin(), wanted.cend());
	  print(secret, found1);

	  constexpr auto found2 = std::ranges::find_end(secret, "word"sv);
	  print(secret, found2);

	  const auto found3 = std::ranges::find_end(secret, "ORD"sv,
	      [](const char x, const char y) { // uses a binary predicate
		  return std::tolower(x) == std::tolower(y);
	      });
	  print(secret, found3);

	  const auto found4 = std::ranges::find_end(secret, "SWORD"sv, {}, {},
	      [](char c) { return std::tolower(c); }); // projects the 2nd range
	  print(secret, found4);

	  static_assert(std::ranges::find_end(secret,  "PASS"sv).empty()); // =>
     not found
      }

Output:
      In "password password word..." found "password" at position [9..17)
		   ^^^^^^^^
      In "password password word..." found "word" at position [18..22)
			    ^^^^
      In "password password word..." found "ord" at position [19..22)
			     ^^^
      In "password password word..." found "sword" at position [12..17)
		      ^^^^^

See also
	ranges::find_last
	ranges::find_last_if
	ranges::find_last_if_not finds the last element satisfying specific cri-
     teria
	(C++23) 		 (niebloid)
	(C++23)
	(C++23)
	ranges::find
	ranges::find_if
	ranges::find_if_not	 finds the  first  element  satisfying	specific
     criteria
	(C++20) 		 (niebloid)
	(C++20)
	(C++20)
	ranges::find_first_of	 searches for any one of a set of elements
	(C++20) 		 (niebloid)
	ranges::adjacent_find	  finds  the  first  two adjacent items that are
     equal (or
	(C++20) 		 satisfy a given predicate)
				 (niebloid)
	ranges::search		 searches for a range of elements
	(C++20) 		 (niebloid)
	ranges::search_n	 searches for a number consecutive copies of  an
     element in a
	(C++20) 		 range
				 (niebloid)
	find_end		  finds  the last sequence of elements in a cer-
     tain range
				 (function template)

http://cppreference.com 	   2024.06.10		std::ranges::find_end(3)
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