std::ranges::is_partitioned
Defined in header <algorithm> |
||
|---|---|---|
| Call signature | ||
template< std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred >
constexpr bool is_partitioned( I first, S last, Pred pred, Proj proj = {} ); |
(1) | (since C++20) |
template< ranges::input_range R, class Proj = std::identity,
std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>> Pred >
constexpr bool is_partitioned( R&& r, Pred pred, Proj proj = {} ); |
(2) | (since C++20) |
1) Returns
true if all elements in the range
[first, last) that satisfy the predicate
p after projection appear before all elements that don't. Also returns
true if
[first, last) is empty.
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 | - | iterator-sentinel pair denoting the range of elements to examine |
| r | - | the range of elements to examine |
| pred | - | predicate to apply to the projected elements |
| proj | - | projection to apply to the elements |
Return value
true if the range [first, last) is empty or is partitioned by p. false otherwise.
Complexity
At most ranges::distance(first, last) applications of pred and proj.
Possible implementation
struct is_partitioned_fn {
template<std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred>
constexpr bool operator()(I first, S last, Pred pred, Proj proj = {}) const
{
for (; first != last; ++first) {
if (!std::invoke(pred, std::invoke(proj, *first))) {
break;
}
}
for (; first != last; ++first) {
if (std::invoke(pred, std::invoke(proj, *first))) {
return false;
}
}
return true;
}
template<ranges::input_range R, class Proj = std::identity,
std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>> Pred>
constexpr bool operator()(R&& r, Pred pred, Proj proj = {}) const
{
return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj));
}
};
inline constexpr auto is_partitioned = is_partitioned_fn();
|
Example
#include <algorithm>
#include <array>
#include <iostream>
#include <utility>
int main()
{
std::array<int, 9> v;
auto is_even = [](int i){ return i % 2 == 0; };
auto print = [&](bool o) {
for (int x : v) std::cout << x << ' ';
std::cout << (o ? "=> " : "=> not ") << "partitioned\n";
};
std::iota(v.begin(), v.end(), 1);
print(std::ranges::is_partitioned(v, is_even));
std::ranges::partition(v, is_even);
print(std::ranges::is_partitioned(std::as_const(v), is_even));
std::ranges::reverse(v);
print(std::ranges::is_partitioned(v.cbegin(), v.cend(), is_even));
print(std::ranges::is_partitioned(v.crbegin(), v.crend(), is_even));
}
Output:
1 2 3 4 5 6 7 8 9 => not partitioned 2 4 6 8 5 3 7 1 9 => partitioned 9 1 7 3 5 8 6 4 2 => not partitioned 9 1 7 3 5 8 6 4 2 => partitioned
See also
|
(C++20)
|
divides a range of elements into two groups (niebloid) |
|
(C++20)
|
locates the partition point of a partitioned range (niebloid) |
|
(C++11)
|
determines if the range is partitioned by the given predicate (function template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/algorithm/ranges/is_partitioned
