prev_permutation

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##### prev_permutation

###### Prototype

    template<class BidirectionalRange>
    bool prev_permutation(BidirectionalRange& rng);

    template<class BidirectionalRange>
    bool prev_permutation(const BidirectionalRange& rng);

    template<class BidirectionalRange, class Compare>
    bool prev_permutation(BidirectionalRange& rng, Compare pred);

    template<class BidirectionalRange, class Compare>
    bool prev_permutation(const BidirectionalRange& rng, Compare pred);

###### Description

`prev_permutation` transforms the range of elements `rng` into the lexicographically next smaller permutation of the elements if such a permutation exists. If one does not exist then the range is transformed into the lexicographically largest permutation and `false` is returned. `true` is returned when the next smaller permutation is successfully generated.

The ordering relationship is determined by using `operator<` in the non-predicate versions, and by evaluating `pred` in the predicate versions.

###### Definition

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

###### Requirements

For the non-predicate versions:

- `BidirectionalRange` is a model of the Bidirectional Range Concept.
- `BidirectionalRange` is mutable.
- `BidirectionalRange`'s value type is a model of the `LessThanComparableConcept`.
- The ordering of objects of type `BidirectionalRange`'s value type is a strict weak ordering, as defined in the `LessThanComparableConcept` requirements.

For the predicate versions:

- `BidirectionalRange` is a model of the Bidirectional Range Concept.
- `BidirectionalRange` is mutable.
- `Compare` is a model of the `StrictWeakOrderingConcept`.
- `BidirectionalRange`'s value type is convertible to both of `Compare`'s argument types.

###### Complexity

Linear. At most `distance(rng) / 2` swaps.