Difference between revisions of "cpp/algorithm/is partitioned"
From cppreference.com
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Revision as of 07:12, 9 January 2021
| Defined in header <algorithm>
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||
| (1) | ||
template< class InputIt, class UnaryPredicate > bool is_partitioned( InputIt first, InputIt last, UnaryPredicate p ); |
(since C++11) (until C++20) |
|
| template< class InputIt, class UnaryPredicate > constexpr bool is_partitioned( InputIt first, InputIt last, UnaryPredicate p ); |
(since C++20) | |
| template< class ExecutionPolicy, class ForwardIt, class UnaryPredicate > bool is_partitioned( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, UnaryPredicate p ); |
(2) | (since C++17) |
1) Returns true if all elements in the range
[first, last) that satisfy the predicate p appear before all elements that don't. Also returns true if [first, last) is empty.2) Same as (1), but executed according to
policy. This overload participates in overload resolution only if |
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. |
(until C++20) |
|
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. |
(since C++20) |
Contents |
Parameters
| first, last | - | the range of elements to check |
| policy | - | the execution policy to use. See execution policy for details. |
| p | - | unary predicate which returns true for the elements expected to be found in the beginning of the range. The expression p(v) must be convertible to bool for every argument |
| Type requirements | ||
-InputIt must meet the requirements of LegacyInputIterator.
| ||
-ForwardIt must meet the requirements of LegacyForwardIterator. and its value type must be convertible to UnaryPredicate's argument type
| ||
-UnaryPredicate must meet the requirements of Predicate.
| ||
Return value
true if the range [first, last) is empty or is partitioned by p. false otherwise.
Complexity
At most std::distance(first, last) applications of p.
Exceptions
The overload with a template parameter named ExecutionPolicy reports errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicyis one of the standard policies, std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Possible implementation
template< class InputIt, class UnaryPredicate > bool is_partitioned(InputIt first, InputIt last, UnaryPredicate p) { for (; first != last; ++first) if (!p(*first)) break; for (; first != last; ++first) if (p(*first)) return false; return true; } |
Example
Run this code
#include <algorithm> #include <array> #include <iostream> int main() { std::array<int, 9> v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; auto is_even = [](int i){ return i % 2 == 0; }; std::cout.setf(std::ios_base::boolalpha); std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' '; std::partition(v.begin(), v.end(), is_even); std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' '; std::reverse(v.begin(), v.end()); std::cout << std::is_partitioned(v.cbegin(), v.cend(), is_even) << ' '; std::cout << std::is_partitioned(v.crbegin(), v.crend(), is_even) << '\n'; }
Output:
false true false true
See also
| divides a range of elements into two groups (function template) | |
| (C++11) |
locates the partition point of a partitioned range (function template) |
| (C++20) |
determines if the range is partitioned by the given predicate (niebloid) |
