stable_partition

quote from : http://en.cppreference.com/w/cpp/algorithm/stable_partition

std::stable_partition

 

C++

 

Algorithm library

 

Defined in header <algorithm>

  template< class BidirIt, class UnaryPredicate >
BidirIt stable_partition( BidirIt first, BidirIt last, UnaryPredicate p );(1) template< class ExecutionPolicy, class BidirIt, class UnaryPredicate >
BidirIt stable_partition( ExecutionPolicy&& policy, BidirIt first, BidirIt last, UnaryPredicate p );(2)(since C++17)   

1) Reorders the elements in the range [first, last) in such a way that all elements for which the predicate preturns true precede the elements for which predicate p returns false. Relative order of the elements is preserved.

2) Same as (1), but executed according to policy. This overload does not participate in overload resolution unlessstd::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last-the range of elements to reorderpolicy-the execution policy to use. See execution policy for details.p-unary predicate which returns ​true if the element should be ordered before other elements. 

The signature of the predicate function should be equivalent to the following:

 bool pred(const Type &a);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type Type must be such that an object of type BidirIt can be dereferenced and then implicitly converted to Type. ​

Type requirements-

BidirIt must meet the requirements of ValueSwappable and BidirectionalIterator.-

The type of dereferenced BidirIt must meet the requirements of MoveAssignable and MoveConstructible.-

UnaryPredicate must meet the requirements of Predicate.

Return value

Iterator to the first element of the second group

Complexity

Exactly last-first applications of the predicate and at most (last-first)*log(last-first) swaps if there is insufficient memory or linear number of swaps if sufficient memory is available.

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,

• if policy is std::parallel_vector_execution_policy, std::terminate is called
• if policy is std::sequential_execution_policy or std::parallel_execution_policy, the algorithm exits with an std::exception_list containing all uncaught exceptions. If there was only one uncaught exception, the algorithm may rethrow it without wrapping in std::exception_list. It is unspecified how much work the algorithm will perform before returning after the first exception was encountered.
• if policy is some other type, the behavior is implementation-defined

• If the algorithm fails to allocate memory (either for itself or to construct an std::exception_list when handling a user exception), std::bad_alloc is thrown.

Notes

This function attempts to allocate a temporary buffer, typically by calling std::get_temporary_buffer. If the allocation fails, the less efficient algorithm is chosen.