std::ranges::adjacent_find - cppreference.com (original) (raw)

Searches the range [first, last) for the first two consecutive equal elements.

1. Elements are compared using pred (after projecting with the projection proj).

2. Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

The function-like entities described on this page are algorithm function objects (informally known as 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 inhibited.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Possible implementation
• 5 Example
• 6 See also

[edit] Parameters

[edit] Return value

An iterator to the first of the first pair of identical elements, that is, the first iterator it such that bool(std::invoke(pred, std::invoke(proj1, *it), std::invoke(proj, *(it + 1)))) is true.

If no such elements are found, an iterator equal to last is returned.

[edit] Complexity

Exactly min((result - first) + 1, (last - first) - 1) applications of the predicate and projection where result is the return value.

[edit] Possible implementation

struct adjacent_find_fn { template<std::forward_iterator I, std::sentinel_for S, class Proj = std::identity, std::indirect_binary_predicate< std::projected<I, Proj>, std::projected<I, Proj>> Pred = ranges::equal_to> constexpr I operator()(I first, S last, Pred pred = {}, Proj proj = {}) const { if (first == last) return first; auto next = ranges::next(first); for (; next != last; ++next, ++first) if (std::invoke(pred, std::invoke(proj, *first), std::invoke(proj, *next))) return first; return next; }   template<ranges::forward_range R, class Proj = std::identity, std::indirect_binary_predicate< std::projected<ranges::iterator_t, Proj>, std::projected<ranges::iterator_t, Proj>> Pred = ranges::equal_to> constexpr ranges::borrowed_iterator_t operator()(R&& r, Pred pred = {}, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr adjacent_find_fn adjacent_find;

[edit] Example

#include #include #include #include   constexpr bool some_of(auto&& r, auto&& pred) // some but not all { return std::ranges::cend(r) != std::ranges::adjacent_find(r, [&pred](auto const& x, auto const& y) { return pred(x) != pred(y); }); }   // test some_of constexpr auto a = {0, 0, 0, 0}, b = {1, 1, 1, 0}, c = {1, 1, 1, 1}; auto is_one = [](auto x){ return x == 1; }; static_assert(!some_of(a, is_one) && some_of(b, is_one) && !some_of(c, is_one));   int main() { const auto v = {0, 1, 2, 3, 40, 40, 41, 41, 5}; /* ^^ ^^ */ namespace ranges = std::ranges;   if (auto it = ranges::adjacent_find(v.begin(), v.end()); it == v.end()) std::cout << "No matching adjacent elements\n"; else std::cout << "The first adjacent pair of equal elements is at [" << ranges::distance(v.begin(), it) << "] == " << *it << '\n';   if (auto it = ranges::adjacent_find(v, ranges::greater()); it == v.end()) std::cout << "The entire vector is sorted in ascending order\n"; else std::cout << "The last element in the non-decreasing subsequence is at [" << ranges::distance(v.begin(), it) << "] == " << *it << '\n'; }

Output:

The first adjacent pair of equal elements is at [4] == 40 The last element in the non-decreasing subsequence is at [7] == 41

[edit] See also

| | removes consecutive duplicate elements in a range(algorithm function object)[edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | | finds the first two adjacent items that are equal (or satisfy a given predicate) (function template) [edit] |