// (C) Copyright Jeremy Siek 2001.

// Distributed under the Boost Software License, Version 1.0. (See

// accompanying file LICENSE_1_0.txt or copy at

// http://www.boost.org/LICENSE_1_0.txt)

#ifndef BOOST_PERMUTATION_HPP

#define BOOST_PERMUTATION_HPP

#include <vector>

#include <memory>

#include <functional>

#include <algorithm>

#include <boost/graph/detail/shadow_iterator.hpp>

namespace boost {

template <class Iter1, class Iter2>

void permute_serial(Iter1 permuter, Iter1 last, Iter2 result)

{

#ifdef BOOST_NO_STD_ITERATOR_TRAITS

  typedef std::ptrdiff_t D:

#else

  typedef typename std::iterator_traits<Iter1>::difference_type D;

#endif

  D n = 0;

  while (permuter != last) {

    std::swap(result[n], result[*permuter]);

    ++n;

    ++permuter;

  }

}

template <class InIter, class RandIterP, class RandIterR>

void permute_copy(InIter first, InIter last, RandIterP p, RandIterR result)

{

#ifdef BOOST_NO_STD_ITERATOR_TRAITS

  typedef std::ptrdiff_t i = 0;

#else

  typename std::iterator_traits<RandIterP>::difference_type i = 0;

#endif

  for (; first != last; ++first, ++i)

    result[p[i]] = *first;

}

namespace detail {

template <class RandIter, class RandIterPerm, class D, class T>

void permute_helper(RandIter first, RandIter last, RandIterPerm p, D, T)

{

  D i = 0, pi, n = last - first, cycle_start;

  T tmp;

  std::vector<int> visited(n, false);

  while (i != n) { // continue until all elements have been processed

    cycle_start = i;

    tmp = first[i];

    do { // walk around a cycle

      pi = p[i];

      visited[pi] = true;

      std::swap(tmp, first[pi]);

      i = pi;

    } while (i != cycle_start);

    // find the next cycle

    for (i = 0; i < n; ++i)

      if (visited[i] == false)

        break;

  }

}

} // namespace detail

template <class RandIter, class RandIterPerm>

void permute(RandIter first, RandIter last, RandIterPerm p)

{

  detail::permute_helper(first, last, p, last - first, *first);

}

// Knuth 1.3.3, Vol. 1 p 176

// modified for zero-based arrays

// time complexity?

//

// WARNING: T must be a signed integer!

template <class PermIter>

void invert_permutation(PermIter X, PermIter Xend)

{

#ifdef BOOST_NO_STD_ITERATOR_TRAITS

  typedef std::ptrdiff_t T:

#else

  typedef typename std::iterator_traits<PermIter>::value_type T;

#endif

  T n = Xend - X;

  T m = n;

  T j = -1;

  while (m > 0) {

    T i = X[m-1] + 1;

    if (i > 0) {

      do {

        X[m-1] = j - 1;

        j = -m;

        m = i;

        i = X[m-1] + 1;

      } while (i > 0);

      i = j;

    }

    X[m-1] = -i - 1;

    --m;

  }

}

// Takes a "normal" permutation array (and its inverse), and turns it

// into a BLAS-style permutation array (which can be thought of as a

// serialized permutation).

template <class Iter1, class Iter2, class Iter3>

inline void serialize_permutation(Iter1 q, Iter1 q_end, Iter2 q_inv, Iter3 p)

{

#ifdef BOOST_NO_STD_ITERATOR_TRAITS

  typedef std::ptrdiff_t P1;

  typedef std::ptrdiff_t P2;

  typedef std::ptrdiff_t D;

#else

  typedef typename std::iterator_traits<Iter1>::value_type P1;

  typedef typename std::iterator_traits<Iter2>::value_type P2;

  typedef typename std::iterator_traits<Iter1>::difference_type D;

#endif

  D n = q_end - q;

  for (D i = 0; i < n; ++i) {

    P1 qi = q[i];

    P2 qii = q_inv[i];

    *p++ = qii;

    std::swap(q[i], q[qii]);

    std::swap(q_inv[i], q_inv[qi]);

  }

}

// Not used anymore, leaving it here for future reference.

template <typename Iter, typename Compare>

void merge_sort(Iter first, Iter last, Compare cmp)

{

  if (first + 1 < last) {

    Iter mid = first + (last - first)/2;

    merge_sort(first, mid, cmp);

    merge_sort(mid, last, cmp);

    std::inplace_merge(first, mid, last, cmp);

  }

}

// time: N log N + 3N + ?

// space: 2N

template <class Iter, class IterP, class Cmp, class Alloc>

inline void sortp(Iter first, Iter last, IterP p, Cmp cmp, Alloc alloc)

{

  typedef typename std::iterator_traits<IterP>::value_type P;

  typedef typename std::iterator_traits<IterP>::difference_type D;

  D n = last - first;

  std::vector<P, Alloc> q(n);

  for (D i = 0; i < n; ++i) 

    q[i] = i;

  std::sort(make_shadow_iter(first, q.begin()),

            make_shadow_iter(last, q.end()),

            shadow_cmp<Cmp>(cmp));

  invert_permutation(q.begin(), q.end());

  std::copy(q.begin(), q.end(), p);

}

template <class Iter, class IterP, class Cmp>

inline void sortp(Iter first, Iter last, IterP p, Cmp cmp)

{

  typedef typename std::iterator_traits<IterP>::value_type P;  

  sortp(first, last, p, cmp, std::allocator<P>());

}

template <class Iter, class IterP>

inline void sortp(Iter first, Iter last, IterP p)

{

  typedef typename std::iterator_traits<Iter>::value_type T;  

  typedef typename std::iterator_traits<IterP>::value_type P;  

  sortp(first, last, p, std::less<T>(), std::allocator<P>());

}

template <class Iter, class IterP, class Cmp, class Alloc>

inline void sortv(Iter first, Iter last, IterP p, Cmp cmp, Alloc alloc)

{

  typedef typename std::iterator_traits<IterP>::value_type P;

  typedef typename std::iterator_traits<IterP>::difference_type D;

  D n = last - first;

  std::vector<P, Alloc> q(n), q_inv(n);

  for (D i = 0; i < n; ++i) 

    q_inv[i] = i;

  std::sort(make_shadow_iter(first, q_inv.begin()), 

            make_shadow_iter(last, q_inv.end()), 

            shadow_cmp<Cmp>(cmp));

  std::copy(q_inv, q_inv.end(), q.begin());

  invert_permutation(q.begin(), q.end());

  serialize_permutation(q.begin(), q.end(), q_inv.end(), p);

}

} // namespace boost

#endif // BOOST_PERMUTATION_HPP