std::partition (3) - Linux Man Pages
Defined in header <algorithm>
template< class BidirIt, class UnaryPredicate > (until C++11)
BidirIt partition( BidirIt first, BidirIt last, UnaryPredicate p );
template< class ForwardIt, class UnaryPredicate > (since C++11)
ForwardIt partition( ForwardIt first, ForwardIt last, UnaryPredicate p ); (until C++20)
template< class ForwardIt, class UnaryPredicate > (1) (since C++20)
constexpr ForwardIt partition( ForwardIt first, ForwardIt last, UnaryPredicate p );
template< class ExecutionPolicy, class ForwardIt, class UnaryPredicate >
ForwardIt partition( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt first, ForwardIt last, UnaryPredicate p );
1) Reorders the elements in the range [first, last) in such a way that all elements for which the predicate p returns true precede the elements for which predicate p returns false. Relative order of the elements is not preserved.
2) Same as (1), but executed according to policy. This overload does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true
first, last - the range of elements to reorder
policy - the execution policy to use. See execution_policy for details.
p - The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of ForwardIt, regardless of value_category, and must not modify v. Thus, a parameter type of VT&is not allowed
BidirIt must meet the requirements of LegacyBidirectionalIterator.
ForwardIt must meet the requirements of ValueSwappable and LegacyForwardIterator. However, the operation is more efficient if ForwardIt also satisfies the requirements of LegacyBidirectionalIterator
UnaryPredicate must meet the requirements of Predicate.
Iterator to the first element of the second group.
Given N = std::distance(first,last),
1) Exactly N applications of the predicate. At most N/2 swaps if ForwardIt meets the requirements of LegacyBidirectionalIterator, and at most N swaps otherwise.
2) O(N log N) swaps and O(N) applications of the predicate.
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 ExecutionPolicy is one of the standard_policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.
// Run this code