lemon/radix_heap.h
author Alpar Juttner <alpar@cs.elte.hu>
Mon, 31 Aug 2009 07:22:26 +0200
changeset 692 33f417de9e70
parent 681 532697c9fa53
child 709 0747f332c478
permissions -rw-r--r--
Merge
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/* -*- mode: C++; indent-tabs-mode: nil; -*-
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 *
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 * This file is a part of LEMON, a generic C++ optimization library.
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 *
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 * Copyright (C) 2003-2009
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 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
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 * (Egervary Research Group on Combinatorial Optimization, EGRES).
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 *
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 * Permission to use, modify and distribute this software is granted
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 * provided that this copyright notice appears in all copies. For
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 * precise terms see the accompanying LICENSE file.
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 *
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 * This software is provided "AS IS" with no warranty of any kind,
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 * express or implied, and with no claim as to its suitability for any
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 * purpose.
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 *
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 */
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#ifndef LEMON_RADIX_HEAP_H
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#define LEMON_RADIX_HEAP_H
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///\ingroup auxdat
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///\file
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///\brief Radix Heap implementation.
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#include <vector>
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#include <lemon/error.h>
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namespace lemon {
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  /// \ingroup auxdata
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  ///
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  /// \brief A Radix Heap implementation.
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  ///
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  /// This class implements the \e radix \e heap data structure. A \e heap
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  /// is a data structure for storing items with specified values called \e
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  /// priorities in such a way that finding the item with minimum priority is
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  /// efficient. This heap type can store only items with \e int priority.
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  /// In a heap one can change the priority of an item, add or erase an
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  /// item, but the priority cannot be decreased under the last removed
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  /// item's priority.
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  ///
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  /// \param IM A read and writable Item int map, used internally
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  /// to handle the cross references.
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  ///
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  /// \see BinHeap
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  /// \see Dijkstra
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  template <typename IM>
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  class RadixHeap {
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  public:
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    typedef typename IM::Key Item;
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    typedef int Prio;
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    typedef IM ItemIntMap;
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    /// \brief Exception thrown by RadixHeap.
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    ///
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    /// This Exception is thrown when a smaller priority
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    /// is inserted into the \e RadixHeap then the last time erased.
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    /// \see RadixHeap
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    class UnderFlowPriorityError : public Exception {
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    public:
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      virtual const char* what() const throw() {
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        return "lemon::RadixHeap::UnderFlowPriorityError";
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      }
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    };
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    /// \brief Type to represent the items states.
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    ///
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    /// Each Item element have a state associated to it. It may be "in heap",
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    /// "pre heap" or "post heap". The latter two are indifferent from the
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    /// heap's point of view, but may be useful to the user.
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    ///
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    /// The ItemIntMap \e should be initialized in such way that it maps
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    /// PRE_HEAP (-1) to any element to be put in the heap...
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    enum State {
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      IN_HEAP = 0,
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      PRE_HEAP = -1,
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      POST_HEAP = -2
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    };
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  private:
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    struct RadixItem {
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      int prev, next, box;
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      Item item;
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      int prio;
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      RadixItem(Item _item, int _prio) : item(_item), prio(_prio) {}
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    };
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    struct RadixBox {
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      int first;
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      int min, size;
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      RadixBox(int _min, int _size) : first(-1), min(_min), size(_size) {}
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    };
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    std::vector<RadixItem> data;
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    std::vector<RadixBox> boxes;
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    ItemIntMap &_iim;
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  public:
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    /// \brief The constructor.
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    ///
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    /// The constructor.
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    ///
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    /// \param map It should be given to the constructor, since it is used
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    /// internally to handle the cross references. The value of the map
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    /// should be PRE_HEAP (-1) for each element.
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    ///
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    /// \param minimal The initial minimal value of the heap.
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    /// \param capacity It determines the initial capacity of the heap.
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    RadixHeap(ItemIntMap &map, int minimal = 0, int capacity = 0)
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      : _iim(map) {
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      boxes.push_back(RadixBox(minimal, 1));
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      boxes.push_back(RadixBox(minimal + 1, 1));
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      while (lower(boxes.size() - 1, capacity + minimal - 1)) {
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        extend();
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      }
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    }
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    /// The number of items stored in the heap.
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    ///
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    /// \brief Returns the number of items stored in the heap.
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    int size() const { return data.size(); }
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    /// \brief Checks if the heap stores no items.
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    ///
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    /// Returns \c true if and only if the heap stores no items.
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    bool empty() const { return data.empty(); }
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    /// \brief Make empty this heap.
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    ///
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    /// Make empty this heap. It does not change the cross reference
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    /// map.  If you want to reuse a heap what is not surely empty you
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    /// should first clear the heap and after that you should set the
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    /// cross reference map for each item to \c PRE_HEAP.
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    void clear(int minimal = 0, int capacity = 0) {
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      data.clear(); boxes.clear();
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      boxes.push_back(RadixBox(minimal, 1));
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      boxes.push_back(RadixBox(minimal + 1, 1));
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      while (lower(boxes.size() - 1, capacity + minimal - 1)) {
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        extend();
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      }
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    }
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  private:
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    bool upper(int box, Prio pr) {
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      return pr < boxes[box].min;
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    }
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    bool lower(int box, Prio pr) {
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      return pr >= boxes[box].min + boxes[box].size;
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    }
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    /// \brief Remove item from the box list.
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    void remove(int index) {
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      if (data[index].prev >= 0) {
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        data[data[index].prev].next = data[index].next;
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      } else {
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        boxes[data[index].box].first = data[index].next;
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      }
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      if (data[index].next >= 0) {
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        data[data[index].next].prev = data[index].prev;
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      }
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    }
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    /// \brief Insert item into the box list.
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    void insert(int box, int index) {
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      if (boxes[box].first == -1) {
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        boxes[box].first = index;
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        data[index].next = data[index].prev = -1;
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      } else {
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        data[index].next = boxes[box].first;
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        data[boxes[box].first].prev = index;
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        data[index].prev = -1;
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        boxes[box].first = index;
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      }
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      data[index].box = box;
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    }
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    /// \brief Add a new box to the box list.
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    void extend() {
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      int min = boxes.back().min + boxes.back().size;
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      int bs = 2 * boxes.back().size;
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      boxes.push_back(RadixBox(min, bs));
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    }
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    /// \brief Move an item up into the proper box.
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    void bubble_up(int index) {
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      if (!lower(data[index].box, data[index].prio)) return;
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      remove(index);
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      int box = findUp(data[index].box, data[index].prio);
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      insert(box, index);
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    }
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    /// \brief Find up the proper box for the item with the given prio.
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    int findUp(int start, int pr) {
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      while (lower(start, pr)) {
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        if (++start == int(boxes.size())) {
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          extend();
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        }
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      }
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      return start;
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    }
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    /// \brief Move an item down into the proper box.
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    void bubble_down(int index) {
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      if (!upper(data[index].box, data[index].prio)) return;
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      remove(index);
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      int box = findDown(data[index].box, data[index].prio);
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      insert(box, index);
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    }
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    /// \brief Find up the proper box for the item with the given prio.
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    int findDown(int start, int pr) {
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      while (upper(start, pr)) {
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        if (--start < 0) throw UnderFlowPriorityError();
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      }
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      return start;
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    }
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    /// \brief Find the first not empty box.
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    int findFirst() {
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      int first = 0;
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      while (boxes[first].first == -1) ++first;
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      return first;
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    }
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    /// \brief Gives back the minimal prio of the box.
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    int minValue(int box) {
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      int min = data[boxes[box].first].prio;
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      for (int k = boxes[box].first; k != -1; k = data[k].next) {
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        if (data[k].prio < min) min = data[k].prio;
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      }
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      return min;
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    }
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    /// \brief Rearrange the items of the heap and makes the
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    /// first box not empty.
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    void moveDown() {
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      int box = findFirst();
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      if (box == 0) return;
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      int min = minValue(box);
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      for (int i = 0; i <= box; ++i) {
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        boxes[i].min = min;
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        min += boxes[i].size;
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      }
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      int curr = boxes[box].first, next;
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      while (curr != -1) {
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        next = data[curr].next;
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        bubble_down(curr);
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        curr = next;
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      }
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    }
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    void relocate_last(int index) {
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      if (index != int(data.size()) - 1) {
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        data[index] = data.back();
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        if (data[index].prev != -1) {
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          data[data[index].prev].next = index;
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        } else {
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          boxes[data[index].box].first = index;
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        }
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        if (data[index].next != -1) {
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          data[data[index].next].prev = index;
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        }
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        _iim[data[index].item] = index;
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      }
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      data.pop_back();
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    }
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  public:
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    /// \brief Insert an item into the heap with the given priority.
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    ///
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    /// Adds \c i to the heap with priority \c p.
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    /// \param i The item to insert.
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    /// \param p The priority of the item.
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    void push(const Item &i, const Prio &p) {
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      int n = data.size();
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      _iim.set(i, n);
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      data.push_back(RadixItem(i, p));
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      while (lower(boxes.size() - 1, p)) {
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        extend();
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      }
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      int box = findDown(boxes.size() - 1, p);
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      insert(box, n);
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    }
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    /// \brief Returns the item with minimum priority.
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    ///
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    /// This method returns the item with minimum priority.
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    /// \pre The heap must be nonempty.
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    Item top() const {
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      const_cast<RadixHeap<ItemIntMap>&>(*this).moveDown();
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      return data[boxes[0].first].item;
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    }
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    /// \brief Returns the minimum priority.
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    ///
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    /// It returns the minimum priority.
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    /// \pre The heap must be nonempty.
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    Prio prio() const {
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      const_cast<RadixHeap<ItemIntMap>&>(*this).moveDown();
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      return data[boxes[0].first].prio;
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     }
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    /// \brief Deletes the item with minimum priority.
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    ///
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    /// This method deletes the item with minimum priority.
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    /// \pre The heap must be non-empty.
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    void pop() {
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      moveDown();
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      int index = boxes[0].first;
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      _iim[data[index].item] = POST_HEAP;
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      remove(index);
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      relocate_last(index);
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    }
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    /// \brief Deletes \c i from the heap.
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    ///
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    /// This method deletes item \c i from the heap, if \c i was
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    /// already stored in the heap.
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    /// \param i The item to erase.
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    void erase(const Item &i) {
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      int index = _iim[i];
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      _iim[i] = POST_HEAP;
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      remove(index);
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      relocate_last(index);
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   }
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    /// \brief Returns the priority of \c i.
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    ///
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    /// This function returns the priority of item \c i.
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    /// \pre \c i must be in the heap.
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    /// \param i The item.
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    Prio operator[](const Item &i) const {
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      int idx = _iim[i];
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      return data[idx].prio;
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    }
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    /// \brief \c i gets to the heap with priority \c p independently
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    /// if \c i was already there.
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    ///
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    /// This method calls \ref push(\c i, \c p) if \c i is not stored
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    /// in the heap and sets the priority of \c i to \c p otherwise.
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    /// It may throw an \e UnderFlowPriorityException.
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    /// \param i The item.
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    /// \param p The priority.
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    void set(const Item &i, const Prio &p) {
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      int idx = _iim[i];
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      if( idx < 0 ) {
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        push(i, p);
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      }
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      else if( p >= data[idx].prio ) {
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        data[idx].prio = p;
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        bubble_up(idx);
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      } else {
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        data[idx].prio = p;
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        bubble_down(idx);
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      }
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    }
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    /// \brief Decreases the priority of \c i to \c p.
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    ///
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    /// This method decreases the priority of item \c i to \c p.
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    /// \pre \c i must be stored in the heap with priority at least \c p, and
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    /// \c should be greater or equal to the last removed item's priority.
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    /// \param i The item.
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    /// \param p The priority.
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    void decrease(const Item &i, const Prio &p) {
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      int idx = _iim[i];
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      data[idx].prio = p;
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      bubble_down(idx);
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    }
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    /// \brief Increases the priority of \c i to \c p.
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    ///
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    /// This method sets the priority of item \c i to \c p.
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    /// \pre \c i must be stored in the heap with priority at most \c p
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    /// \param i The item.
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    /// \param p The priority.
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    void increase(const Item &i, const Prio &p) {
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      int idx = _iim[i];
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      data[idx].prio = p;
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      bubble_up(idx);
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    }
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    /// \brief Returns if \c item is in, has already been in, or has
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    /// never been in the heap.
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    ///
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    /// This method returns PRE_HEAP if \c item has never been in the
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    /// heap, IN_HEAP if it is in the heap at the moment, and POST_HEAP
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    /// otherwise. In the latter case it is possible that \c item will
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    /// get back to the heap again.
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    /// \param i The item.
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    State state(const Item &i) const {
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      int s = _iim[i];
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      if( s >= 0 ) s = 0;
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      return State(s);
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    }
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    /// \brief Sets the state of the \c item in the heap.
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    ///
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    /// Sets the state of the \c item in the heap. It can be used to
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    /// manually clear the heap when it is important to achive the
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    /// better time complexity.
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    /// \param i The item.
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    /// \param st The state. It should not be \c IN_HEAP.
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    void state(const Item& i, State st) {
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      switch (st) {
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      case POST_HEAP:
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      case PRE_HEAP:
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        if (state(i) == IN_HEAP) {
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          erase(i);
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        }
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        _iim[i] = st;
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        break;
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      case IN_HEAP:
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        break;
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      }
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    }
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  }; // class RadixHeap
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} // namespace lemon
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#endif // LEMON_RADIX_HEAP_H