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std::ranges::adjacent_find(3) | C++ Standard Libary | std::ranges::adjacent_find(3) |
NAME¶
std::ranges::adjacent_find - std::ranges::adjacent_find
Synopsis¶
Defined in header <algorithm>
Call signature
template< std::forward_iterator I, std::sentinel_for<I> S, class
Proj = std::identity,
std::indirect_binary_predicate<
std::projected<I, Proj>, (1) (since C++20)
std::projected<I, Proj>> Pred = ranges::equal_to >
constexpr I adjacent_find( I first, S last, Pred pred = {}, Proj
proj = {} );
template< ranges::forward_range R, class Proj = std::identity,
std::indirect_binary_predicate<
std::projected<ranges::iterator_t<R>, Proj>,
std::projected<ranges::iterator_t<R>, Proj>> Pred = (2)
(since C++20)
ranges::equal_to >
constexpr ranges::borrowed_iterator_t<R>
adjacent_find( R&& r, Pred pred = {}, Proj proj = {} );
Searches the range [first, last) for 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 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¶
first, last - the range of elements to examine
r - the range of the elements to examine
pred - predicate to apply to the projected elements
proj - projection to apply to the elements
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.
Complexity¶
Exactly min((result-first)+1, (last-first)-1) applications of the
predicate and
projection where result is the return value.
Possible implementation¶
struct adjacent_find_fn {
template< std::forward_iterator I, std::sentinel_for<I> 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 first;
}
template< ranges::forward_range R, class Proj = std::identity,
std::indirect_binary_predicate<
std::projected<ranges::iterator_t<R>, Proj>,
std::projected<ranges::iterator_t<R>, Proj>> Pred =
ranges::equal_to >
constexpr ranges::borrowed_iterator_t<R>
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;
Example¶
// Run this code
#include <algorithm>
#include <iostream>
#include <vector>
#include <functional>
int main()
{
std::vector<int> v1{0, 1, 2, 3, 40, 40, 41, 41, 5};
// ^^ ^^
namespace ranges = std::ranges;
auto i1 = ranges::adjacent_find(v1.begin(), v1.end());
if (i1 == v1.end()) {
std::cout << "No matching adjacent elements\n";
} else {
std::cout << "The first adjacent pair of equal elements is at
["
<< ranges::distance(v1.begin(), i1) << "] == " <<
*i1 << '\n';
}
auto i2 = ranges::adjacent_find(v1, ranges::greater());
if (i2 == v1.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(v1.begin(), i2) << "] == " <<
*i2 << '\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
See also¶
ranges::unique removes consecutive duplicate elements in a range
(C++20) (niebloid)
finds the first two adjacent items that are equal (or satisfy a given
adjacent_find predicate)
(function template)
2022.07.31 | http://cppreference.com |