libcxx/test/std/algorithms/alg.sorting/alg.permutation.generators/prev_permutation.pass.cpp

//===----------------------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

// <algorithm>

// template<BidirectionalIterator Iter>
//   requires ShuffleIterator<Iter>
//         && LessThanComparable<Iter::value_type>
//   bool
//   prev_permutation(Iter first, Iter last);

#include <algorithm>
#include <cassert>

#include "test_iterators.h"

#include <cstdio>

int factorial(int x)
{
    int r = 1;
    for (; x; --x)
        r *= x;
    return r;
}

template <class Iter>
void
test()
{
    int ia[] = {6, 5, 4, 3, 2, 1};
    const int sa = sizeof(ia)/sizeof(ia[0]);
    int prev[sa];
    for (int e = 0; e <= sa; ++e)
    {
        int count = 0;
        bool x;
        do
        {
            std::copy(ia, ia+e, prev);
            x = std::prev_permutation(Iter(ia), Iter(ia+e));
            if (e > 1)
            {
                if (x)
                    assert(std::lexicographical_compare(ia, ia+e, prev, prev+e));
                else
                    assert(std::lexicographical_compare(prev, prev+e, ia, ia+e));
            }
            ++count;
        } while (x);
        assert(count == factorial(e));
    }
}

int main()
{
    test<bidirectional_iterator<int*> >();
    test<random_access_iterator<int*> >();
    test<int*>();
}