/* -*- mode: C++; indent-tabs-mode: nil; -*-
 *
 * This file is a part of LEMON, a generic C++ optimization library.
 *
 * Copyright (C) 2003-2009
 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
 * (Egervary Research Group on Combinatorial Optimization, EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 */

#ifndef RADIX_SORT_H
#define RADIX_SORT_H

/// \ingroup auxalg
/// \file
/// \brief Radix sort
///
/// Linear time sorting algorithms

#include <vector>
#include <limits>
#include <iterator>
#include <algorithm>

namespace lemon {

  namespace _radix_sort_bits {

    template <typename Value>
    struct Identity {
      const Value& operator()(const Value& val) {
        return val;
      }
    };


    template <typename Value, typename Iterator, typename Functor>
    Iterator radixSortPartition(Iterator first, Iterator last,
                                Functor functor, Value mask) {
      while (first != last && !(functor(*first) & mask)) {
        ++first;
      }
      if (first == last) {
        return first;
      }
      --last;
      while (first != last && (functor(*last) & mask)) {
        --last;
      }
      if (first == last) {
        return first;
      }
      std::iter_swap(first, last);
      ++first;
      if (!(first < last)) {
        return first;
      }
      while (true) {
        while (!(functor(*first) & mask)) {
          ++first;
        }
        --last;
        while (functor(*last) & mask) {
          --last;
        }
        if (!(first < last)) {
          return first;
        }
        std::iter_swap(first, last);
        ++first;
      }
    }

    template <typename Iterator, typename Functor>
    Iterator radixSortSignPartition(Iterator first, Iterator last,
                                    Functor functor) {
      while (first != last && functor(*first) < 0) {
        ++first;
      }
      if (first == last) {
        return first;
      }
      --last;
      while (first != last && functor(*last) >= 0) {
        --last;
      }
      if (first == last) {
        return first;
      }
      std::iter_swap(first, last);
      ++first;
      if (!(first < last)) {
        return first;
      }
      while (true) {
        while (functor(*first) < 0) {
          ++first;
        }
        --last;
        while (functor(*last) >= 0) {
          --last;
        }
        if (!(first < last)) {
          return first;
        }
        std::iter_swap(first, last);
        ++first;
      }
    }

    template <typename Value, typename Iterator, typename Functor>
    void radixIntroSort(Iterator first, Iterator last,
                        Functor functor, Value mask) {
      while (mask != 0 && last - first > 1) {
        Iterator cut = radixSortPartition(first, last, functor, mask);
        mask >>= 1;
        radixIntroSort(first, cut, functor, mask);
        first = cut;
      }
    }

    template <typename Value, typename Iterator, typename Functor>
    void radixSignedSort(Iterator first, Iterator last, Functor functor) {

      Iterator cut = radixSortSignPartition(first, last, functor);

      Value mask;
      int max_digit;
      Iterator it;

      mask = ~0; max_digit = 0;
      for (it = first; it != cut; ++it) {
        while ((mask & functor(*it)) != mask) {
          ++max_digit;
          mask <<= 1;
        }
      }
      radixIntroSort(first, cut, functor, 1 << max_digit);

      mask = 0; max_digit = 0;
      for (it = cut; it != last; ++it) {
        while ((mask | functor(*it)) != mask) {
          ++max_digit;
          mask <<= 1; mask |= 1;
        }
      }
      radixIntroSort(cut, last, functor, 1 << max_digit);
    }

    template <typename Value, typename Iterator, typename Functor>
    void radixUnsignedSort(Iterator first, Iterator last, Functor functor) {

      Value mask = 0;
      int max_digit = 0;

      Iterator it;
      for (it = first; it != last; ++it) {
        while ((mask | functor(*it)) != mask) {
          ++max_digit;
          mask <<= 1; mask |= 1;
        }
      }
      radixIntroSort(first, last, functor, 1 << max_digit);
    }


    template <typename Value,
              bool sign = std::numeric_limits<Value>::is_signed >
    struct RadixSortSelector {
      template <typename Iterator, typename Functor>
      static void sort(Iterator first, Iterator last, Functor functor) {
        radixSignedSort<Value>(first, last, functor);
      }
    };

    template <typename Value>
    struct RadixSortSelector<Value, false> {
      template <typename Iterator, typename Functor>
      static void sort(Iterator first, Iterator last, Functor functor) {
        radixUnsignedSort<Value>(first, last, functor);
      }
    };

  }

  /// \ingroup auxalg
  ///
  /// \brief Sorts the STL compatible range into ascending order.
  ///
  /// The \c radixSort sorts an STL compatible range into ascending
  /// order.  The radix sort algorithm can sort items which are mapped
  /// to integers with an adaptable unary function \c functor and the
  /// order will be ascending according to these mapped values.
  ///
  /// It is also possible to use a normal function instead
  /// of the functor object. If the functor is not given it will use
  /// the identity function instead.
  ///
  /// This is a special quick sort algorithm where the pivot
  /// values to split the items are choosen to be 2<sup>k</sup>
  /// for each \c k.
  /// Therefore, the time complexity of the algorithm is O(log(c)*n) and
  /// it uses O(log(c)) additional space, where \c c is the maximal value
  /// and \c n is the number of the items in the container.
  ///
  /// \param first The begin of the given range.
  /// \param last The end of the given range.
  /// \param functor An adaptible unary function or a normal function
  /// which maps the items to any integer type which can be either
  /// signed or unsigned.
  ///
  /// \sa stableRadixSort()
  template <typename Iterator, typename Functor>
  void radixSort(Iterator first, Iterator last, Functor functor) {
    using namespace _radix_sort_bits;
    typedef typename Functor::result_type Value;
    RadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void radixSort(Iterator first, Iterator last, Value (*functor)(Key)) {
    using namespace _radix_sort_bits;
    RadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void radixSort(Iterator first, Iterator last, Value& (*functor)(Key)) {
    using namespace _radix_sort_bits;
    RadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void radixSort(Iterator first, Iterator last, Value (*functor)(Key&)) {
    using namespace _radix_sort_bits;
    RadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void radixSort(Iterator first, Iterator last, Value& (*functor)(Key&)) {
    using namespace _radix_sort_bits;
    RadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator>
  void radixSort(Iterator first, Iterator last) {
    using namespace _radix_sort_bits;
    typedef typename std::iterator_traits<Iterator>::value_type Value;
    RadixSortSelector<Value>::sort(first, last, Identity<Value>());
  }

  namespace _radix_sort_bits {

    template <typename Value>
    unsigned char valueByte(Value value, int byte) {
      return value >> (std::numeric_limits<unsigned char>::digits * byte);
    }

    template <typename Functor, typename Key>
    void stableRadixIntroSort(Key *first, Key *last, Key *target,
                              int byte, Functor functor) {
      const int size =
        unsigned(std::numeric_limits<unsigned char>::max()) + 1;
      std::vector<int> counter(size);
      for (int i = 0; i < size; ++i) {
        counter[i] = 0;
      }
      Key *it = first;
      while (first != last) {
        ++counter[valueByte(functor(*first), byte)];
        ++first;
      }
      int prev, num = 0;
      for (int i = 0; i < size; ++i) {
        prev = num;
        num += counter[i];
        counter[i] = prev;
      }
      while (it != last) {
        target[counter[valueByte(functor(*it), byte)]++] = *it;
        ++it;
      }
    }

    template <typename Functor, typename Key>
    void signedStableRadixIntroSort(Key *first, Key *last, Key *target,
                                    int byte, Functor functor) {
      const int size =
        unsigned(std::numeric_limits<unsigned char>::max()) + 1;
      std::vector<int> counter(size);
      for (int i = 0; i < size; ++i) {
        counter[i] = 0;
      }
      Key *it = first;
      while (first != last) {
        counter[valueByte(functor(*first), byte)]++;
        ++first;
      }
      int prev, num = 0;
      for (int i = size / 2; i < size; ++i) {
        prev = num;
        num += counter[i];
        counter[i] = prev;
      }
      for (int i = 0; i < size / 2; ++i) {
        prev = num;
        num += counter[i];
        counter[i] = prev;
      }
      while (it != last) {
        target[counter[valueByte(functor(*it), byte)]++] = *it;
        ++it;
      }
    }


    template <typename Value, typename Iterator, typename Functor>
    void stableRadixSignedSort(Iterator first, Iterator last, Functor functor) {
      if (first == last) return;
      typedef typename std::iterator_traits<Iterator>::value_type Key;
      typedef std::allocator<Key> Allocator;
      Allocator allocator;

      int length = std::distance(first, last);
      Key* buffer = allocator.allocate(2 * length);
      try {
        bool dir = true;
        std::copy(first, last, buffer);
        for (int i = 0; i < int(sizeof(Value)) - 1; ++i) {
          if (dir) {
            stableRadixIntroSort(buffer, buffer + length, buffer + length,
                                 i, functor);
          } else {
            stableRadixIntroSort(buffer + length, buffer + 2 * length, buffer,
                                 i, functor);
          }
          dir = !dir;
        }
        if (dir) {
          signedStableRadixIntroSort(buffer, buffer + length, buffer + length,
                                     sizeof(Value) - 1, functor);
          std::copy(buffer + length, buffer + 2 * length, first);
        }        else {
          signedStableRadixIntroSort(buffer + length, buffer + 2 * length,
                                     buffer, sizeof(Value) - 1, functor);
          std::copy(buffer, buffer + length, first);
        }
      } catch (...) {
        allocator.deallocate(buffer, 2 * length);
        throw;
      }
      allocator.deallocate(buffer, 2 * length);
    }

    template <typename Value, typename Iterator, typename Functor>
    void stableRadixUnsignedSort(Iterator first, Iterator last,
                                 Functor functor) {
      if (first == last) return;
      typedef typename std::iterator_traits<Iterator>::value_type Key;
      typedef std::allocator<Key> Allocator;
      Allocator allocator;

      int length = std::distance(first, last);
      Key *buffer = allocator.allocate(2 * length);
      try {
        bool dir = true;
        std::copy(first, last, buffer);
        for (int i = 0; i < int(sizeof(Value)); ++i) {
          if (dir) {
            stableRadixIntroSort(buffer, buffer + length,
                                 buffer + length, i, functor);
          } else {
            stableRadixIntroSort(buffer + length, buffer + 2 * length,
                                 buffer, i, functor);
          }
          dir = !dir;
        }
        if (dir) {
          std::copy(buffer, buffer + length, first);
        }        else {
          std::copy(buffer + length, buffer + 2 * length, first);
        }
      } catch (...) {
        allocator.deallocate(buffer, 2 * length);
        throw;
      }
      allocator.deallocate(buffer, 2 * length);
    }



    template <typename Value,
              bool sign = std::numeric_limits<Value>::is_signed >
    struct StableRadixSortSelector {
      template <typename Iterator, typename Functor>
      static void sort(Iterator first, Iterator last, Functor functor) {
        stableRadixSignedSort<Value>(first, last, functor);
      }
    };

    template <typename Value>
    struct StableRadixSortSelector<Value, false> {
      template <typename Iterator, typename Functor>
      static void sort(Iterator first, Iterator last, Functor functor) {
        stableRadixUnsignedSort<Value>(first, last, functor);
      }
    };

  }

  /// \ingroup auxalg
  ///
  /// \brief Sorts the STL compatible range into ascending order in a stable
  /// way.
  ///
  /// This function sorts an STL compatible range into ascending
  /// order according to an integer mapping in the same as radixSort() does.
  ///
  /// This sorting algorithm is stable, i.e. the order of two equal
  /// elements remains the same after the sorting.
  ///
  /// This sort algorithm  use a radix forward sort on the
  /// bytes of the integer number. The algorithm sorts the items
  /// byte-by-byte. First, it counts how many times a byte value occurs
  /// in the container, then it copies the corresponding items to
  /// another container in asceding order in O(n) time.
  ///
  /// The time complexity of the algorithm is O(log(c)*n) and
  /// it uses O(n) additional space, where \c c is the
  /// maximal value and \c n is the number of the items in the
  /// container.
  ///

  /// \param first The begin of the given range.
  /// \param last The end of the given range.
  /// \param functor An adaptible unary function or a normal function
  /// which maps the items to any integer type which can be either
  /// signed or unsigned.
  /// \sa radixSort()
  template <typename Iterator, typename Functor>
  void stableRadixSort(Iterator first, Iterator last, Functor functor) {
    using namespace _radix_sort_bits;
    typedef typename Functor::result_type Value;
    StableRadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void stableRadixSort(Iterator first, Iterator last, Value (*functor)(Key)) {
    using namespace _radix_sort_bits;
    StableRadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void stableRadixSort(Iterator first, Iterator last, Value& (*functor)(Key)) {
    using namespace _radix_sort_bits;
    StableRadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void stableRadixSort(Iterator first, Iterator last, Value (*functor)(Key&)) {
    using namespace _radix_sort_bits;
    StableRadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator, typename Value, typename Key>
  void stableRadixSort(Iterator first, Iterator last, Value& (*functor)(Key&)) {
    using namespace _radix_sort_bits;
    StableRadixSortSelector<Value>::sort(first, last, functor);
  }

  template <typename Iterator>
  void stableRadixSort(Iterator first, Iterator last) {
    using namespace _radix_sort_bits;
    typedef typename std::iterator_traits<Iterator>::value_type Value;
    StableRadixSortSelector<Value>::sort(first, last, Identity<Value>());
  }

}

#endif