std::ranges::is_partitioned() algorithm
- od C++20
- Simplified
- Detailed
// (1)
constexpr bool
is_partitioned( I first, S last, Pred pred, Proj proj = {} );
// (2)
constexpr bool
is_partitioned( R&& r, Pred pred, Proj proj = {} );
The type of arguments are generic and have the following constraints:
I
-std::input_iterator
S
-std::sentinel_for<I>
R
-std::ranges::input_range
Pred
:- (1) -
std::indirect_unary_predicate<std::projected<I, Proj>>
- (2) -
std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>>
- (1) -
Proj
- (none)
The Proj
template argument has a default type std::identity
for all overloads.
// (1)
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 = {} );
// (2)
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 = {} );
-
(1) Returns
true
if all elements in the range [first
;last
) that satisfy the predicate pred 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 range, as if usingranges::begin(r)
asfirst
andranges::end(r)
aslast
.
The function-like entities described on this page are niebloids.
Parameters
first last | The range of elements to process. |
r | The range of elements to process. |
pred | The predicate to apply to the projected elemenets. |
proj | The projection to apply to the elements. |
Return value
If the range is empty or partitioned by p
- true
.
Otherwise, false
.
Complexity
At most ranges::distance(first, last)
applications of pred
and proj
.
Exceptions
(none)
Possible implementation
is_partitioned(1) and is_partitioned(2)
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();
Examples
#include <algorithm>
#include <array>
#include <iostream>
#include <numeric>
#include <utility>
int main()
{
std::array<int, 9> v;
auto print = [&v](bool o)
{
for (int x : v)
std::cout << x << ' ';
std::cout << (o ? "=> " : "=> not ") << "partitioned\n";
};
auto is_even = [](int i) { return i % 2 == 0; };
std::iota(v.begin(), v.end(), 1); // or std::ranges::iota(v, 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));
}
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
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