partition

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##### partition

###### Prototype

    template<
        class ForwardRange,
        class UnaryPredicate
        >
    typename range_iterator<ForwardRange>::type
    partition(ForwardRange& rng, UnaryPredicate pred);

    template<
        class ForwardRange,
        class UnaryPredicate
        >
    typename range_iterator<const ForwardRange>::type
    partition(const ForwardRange& rng, UnaryPredicate pred);

    template<
        range_return_value re,
        class ForwardRange,
        class UnaryPredicate
        >
    typename range_return<ForwardRange, re>::type
    partition(ForwardRange& rng, UnaryPredicate pred);

    template<
        range_return_value re,
        class ForwardRange,
        class UnaryPredicate
        >
    typename range_return<const ForwardRange, re>::type
    partition(const ForwardRange& rng, UnaryPredicate pred);

###### Description

`partition` orders the elements in `rng` based on `pred`, such that the elements that satisfy `pred` precede the elements that do not. In the versions that return a single iterator, the return value is the middle iterator. In the versions that have a configurable range_return, `found` corresponds to the middle iterator.

###### Definition

Defined in the header file `boost/range/algorithm/partition.hpp`

###### Requirements

- `ForwardRange` is a model of the Forward Range Concept. For C++ versions prior to C++11 the underlying std::partition requires Bidirectional Iterators, hence the requirement for older library versions is for a Bidirectional Range.
- `UnaryPredicate` is a model of the `PredicateConcept`.
- `ForwardRange`'s value type is convertible to `UnaryPredicate`'s argument type.

###### Complexity

Linear. Exactly `distance(rng)` applications of `pred`, and at most `distance(rng) / 2` swaps.