COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/lemon/radix_heap.h @ 1344:9146f77f6d67

Last change on this file since 1344:9146f77f6d67 was 1344:9146f77f6d67, checked in by Balazs Dezso, 15 years ago

Removed obsolote todo.

File size: 11.5 KB
Line 
1/* -*- C++ -*-
2 * src/lemon/radix_heap.h - Part of LEMON, a generic C++ optimization library
3 *
4 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
5 * (Egervary Combinatorial Optimization Research Group, EGRES).
6 *
7 * Permission to use, modify and distribute this software is granted
8 * provided that this copyright notice appears in all copies. For
9 * precise terms see the accompanying LICENSE file.
10 *
11 * This software is provided "AS IS" with no warranty of any kind,
12 * express or implied, and with no claim as to its suitability for any
13 * purpose.
14 *
15 */
16
17#ifndef LEMON_RADIX_HEAP_H
18#define LEMON_RADIX_HEAP_H
19
20///\ingroup auxdat
21///\file
22///\brief Radix Heap implementation.
23
24#include <vector>
25#include <lemon/error.h>
26
27namespace lemon {
28
29  /// \addtogroup auxdat
30  /// @{
31
32  /// \brief Exception thrown by RadixHeap.
33  /// 
34  /// This Exception is thrown when a smaller priority
35  /// is inserted into the \e RadixHeap then the last time erased.
36  /// \see RadixHeap
37  /// \author Balazs Dezso
38
39  class UnderFlowPriorityError : public RuntimeError {
40  public:
41    virtual const char* exceptionName() const {
42      return "lemon::UnderFlowPriorityError";
43    } 
44  };
45
46  /// \brief A Radix Heap implementation.
47  ///
48  /// This class implements the \e radix \e heap data structure. A \e heap
49  /// is a data structure for storing items with specified values called \e
50  /// priorities in such a way that finding the item with minimum priority is
51  /// efficient. This heap type can store only items with \e int priority.
52  /// In a heap one can change the priority of an item, add or erase an
53  /// item, but the priority cannot be decreased under the last removed
54  /// item's priority.
55  ///
56  /// \param _Item Type of the items to be stored. 
57  /// \param _ItemIntMap A read and writable Item int map, used internally
58  /// to handle the cross references.
59  ///
60  /// \see BinHeap
61  /// \see Dijkstra
62  /// \author Balazs Dezso
63
64  template <typename _Item, typename _ItemIntMap>
65  class RadixHeap {
66
67  public:
68    typedef _Item Item;
69    typedef int Prio;
70    typedef _ItemIntMap ItemIntMap;
71
72    /// \brief Type to represent the items states.
73    ///
74    /// Each Item element have a state associated to it. It may be "in heap",
75    /// "pre heap" or "post heap". The latter two are indifferent from the
76    /// heap's point of view, but may be useful to the user.
77    ///
78    /// The ItemIntMap \e should be initialized in such way that it maps
79    /// PRE_HEAP (-1) to any element to be put in the heap...
80    enum state_enum {
81      IN_HEAP = 0,
82      PRE_HEAP = -1,
83      POST_HEAP = -2
84    };
85
86  private:
87   
88    struct RadixItem {
89      int prev, next, box;
90      Item item;
91      int prio;
92      RadixItem(Item _item, int _prio) : item(_item), prio(_prio) {}
93    };
94
95    struct RadixBox {
96      int first;
97      int min, size;
98      RadixBox(int _min, int _size) : first(-1), min(_min), size(_size) {}
99    };
100
101    std::vector<RadixItem> data;
102    std::vector<RadixBox> boxes;
103
104    ItemIntMap &iim;
105
106
107  public:
108    /// \brief The constructor.
109    ///
110    /// The constructor.
111    /// \param _iim should be given to the constructor, since it is used
112    /// internally to handle the cross references. The value of the map
113    /// should be PRE_HEAP (-1) for each element.
114    explicit RadixHeap(ItemIntMap &_iim) : iim(_iim) {
115      boxes.push_back(RadixBox(0, 1));
116      boxes.push_back(RadixBox(1, 1));
117    }
118
119    /// \brief The constructor.
120    ///
121    /// The constructor.
122    ///
123    /// \param _iim It should be given to the constructor, since it is used
124    /// internally to handle the cross references. The value of the map
125    /// should be PRE_HEAP (-1) for each element.
126    ///
127    /// \param capacity It determines the initial capacity of the heap.
128    RadixHeap(ItemIntMap &_iim, int capacity) : iim(_iim) {
129      boxes.push_back(RadixBox(0, 1));
130      boxes.push_back(RadixBox(1, 1));
131      while (upper(boxes.back(), capacity)) {
132        extend();
133      }
134    }
135
136    /// The number of items stored in the heap.
137    ///
138    /// \brief Returns the number of items stored in the heap.
139    int size() const { return data.size(); }
140    /// \brief Checks if the heap stores no items.
141    ///
142    /// Returns \c true if and only if the heap stores no items.
143    bool empty() const { return data.empty(); }
144
145  private:
146
147    bool upper(int box, Prio prio) {
148      return prio < boxes[box].min;
149    }
150
151    bool lower(int box, Prio prio) {
152      return prio >= boxes[box].min + boxes[box].size;
153    }
154
155    /// \brief Remove item from the box list.
156    void remove(int index) {
157      if (data[index].prev >= 0) {
158        data[data[index].prev].next = data[index].next;
159      } else {
160        boxes[data[index].box].first = data[index].next;
161      }
162      if (data[index].next >= 0) {
163        data[data[index].next].prev = data[index].prev;
164      }
165    }
166
167    /// \brief Insert item into the box list.
168    void insert(int box, int index) {
169      if (boxes[box].first == -1) {
170        boxes[box].first = index;
171        data[index].next = data[index].prev = -1;
172      } else {
173        data[index].next = boxes[box].first;
174        data[boxes[box].first].prev = index;
175        data[index].prev = -1;
176        boxes[box].first = index;
177      }
178      data[index].box = box;
179    }
180
181    /// \brief Add a new box to the box list.
182    void extend() {
183      int min = boxes.back().min + boxes.back().size;
184      int size = 2 * boxes.back().size;
185      boxes.push_back(RadixBox(min, size));
186    }
187
188    /// \brief Move an item up into the proper box.
189    void bubble_up(int index) {
190      if (!lower(data[index].box, data[index].prio)) return;
191      remove(index);
192      int box = findUp(data[index].box, data[index].prio);
193      insert(box, index);     
194    }
195
196    /// \brief Find up the proper box for the item with the given prio.
197    int findUp(int start, int prio) {
198      while (lower(start, prio)) {
199        if (++start == (int)boxes.size()) {
200          extend();
201        }
202      }
203      return start;
204    }
205
206    /// \brief Move an item down into the proper box.
207    void bubble_down(int index) {
208      if (!upper(data[index].box, data[index].prio)) return;
209      remove(index);
210      int box = findDown(data[index].box, data[index].prio);
211      insert(box, index);
212    }
213
214    /// \brief Find up the proper box for the item with the given prio.
215    int findDown(int start, int prio) {
216      while (upper(start, prio)) {
217        if (--start < 0) throw UnderFlowPriorityError();
218      }
219      return start;
220    }
221
222    /// \brief Find the first not empty box.
223    int findFirst() {
224      int first = 0;
225      while (boxes[first].first == -1) ++first;
226      return first;
227    }
228
229    /// \brief Gives back the minimal prio of the box.
230    int minValue(int box) {
231      int min = data[boxes[box].first].prio;
232      for (int k = boxes[box].first; k != -1; k = data[k].next) {
233        if (data[k].prio < min) min = data[k].prio;
234      }
235      return min;
236    }
237
238    /// \brief Rearrange the items of the heap and makes the
239    /// first box not empty.
240    void moveDown() {
241      int box = findFirst();
242      if (box == 0) return;
243      int min = minValue(box);
244      for (int i = 0; i <= box; ++i) {
245        boxes[i].min = min;
246        min += boxes[i].size;
247      }
248      int curr = boxes[box].first, next;
249      while (curr != -1) {
250        next = data[curr].next;
251        bubble_down(curr);
252        curr = next;
253      }     
254    }
255
256    void relocate_last(int index) {
257      if (index != (int)data.size() - 1) {
258        data[index] = data.back();
259        if (data[index].prev != -1) {
260          data[data[index].prev].next = index;
261        } else {
262          boxes[data[index].box].first = index;
263        }
264        if (data[index].next != -1) {
265          data[data[index].next].prev = index;
266        }
267        iim[data[index].item] = index;
268      }
269      data.pop_back();
270    }
271
272  public:
273
274    /// \brief Insert an item into the heap with the given heap.
275    ///   
276    /// Adds \c i to the heap with priority \c p.
277    /// \param i The item to insert.
278    /// \param p The priority of the item.
279    void push(const Item &i, const Prio &p) {
280      int n = data.size();
281      iim.set(i, n);
282      data.push_back(RadixItem(i, p));
283      while (lower(boxes.size() - 1, p)) {
284        extend();
285      }
286      int box = findDown(boxes.size() - 1, p);
287      insert(box, n);
288    }
289
290    /// \brief Returns the item with minimum priority.
291    ///
292    /// This method returns the item with minimum priority. 
293    /// \pre The heap must be nonempty. 
294    Item top() const {
295      const_cast<RadixHeap<Item, ItemIntMap>*>(this)->moveDown();
296      return data[boxes[0].first].item;
297    }
298
299    /// \brief Returns the minimum priority.
300    ///
301    /// It returns the minimum priority.
302    /// \pre The heap must be nonempty.
303    Prio prio() const {
304      const_cast<RadixHeap<Item, ItemIntMap>*>(this)->moveDown();
305      return data[boxes[0].first].prio;
306     }
307
308    /// \brief Deletes the item with minimum priority.
309    ///
310    /// This method deletes the item with minimum priority.
311    /// \pre The heap must be non-empty. 
312    void pop() {
313      moveDown();
314      int index = boxes[0].first;
315      iim[data[index].item] = POST_HEAP;
316      remove(index);
317      relocate_last(index);
318    }
319
320    /// \brief Deletes \c i from the heap.
321    ///
322    /// This method deletes item \c i from the heap, if \c i was
323    /// already stored in the heap.
324    /// \param i The item to erase.
325    void erase(const Item &i) {
326      int index = iim[i];
327      iim[i] = POST_HEAP;
328      remove(index);
329      relocate_last(index);
330   }
331
332    /// \brief Returns the priority of \c i.
333    ///
334    /// This function returns the priority of item \c i. 
335    /// \pre \c i must be in the heap.
336    /// \param i The item.
337    Prio operator[](const Item &i) const {
338      int idx = iim[i];
339      return data[idx].prio;
340    }
341
342    /// \brief \c i gets to the heap with priority \c p independently
343    /// if \c i was already there.
344    ///
345    /// This method calls \ref push(\c i, \c p) if \c i is not stored
346    /// in the heap and sets the priority of \c i to \c p otherwise.
347    /// It may throw an \e UnderFlowPriorityException.
348    /// \param i The item.
349    /// \param p The priority.
350    void set(const Item &i, const Prio &p) {
351      int idx = iim[i];
352      if( idx < 0 ) {
353        push(i, p);
354      }
355      else if( p >= data[idx].prio ) {
356        data[idx].prio = p;
357        bubble_up(idx);
358      } else {
359        data[idx].prio = p;
360        bubble_down(idx);
361      }
362    }
363
364
365    /// \brief Decreases the priority of \c i to \c p.
366    ///
367    /// This method decreases the priority of item \c i to \c p.
368    /// \pre \c i must be stored in the heap with priority at least \c p, and
369    /// \c should be greater then the last removed item's priority.
370    /// \param i The item.
371    /// \param p The priority.
372    void decrease(const Item &i, const Prio &p) {
373      int idx = iim[i];
374      data[idx].prio = p;
375      bubble_down(idx);
376    }
377
378    /// \brief Increases the priority of \c i to \c p.
379    ///
380    /// This method sets the priority of item \c i to \c p.
381    /// \pre \c i must be stored in the heap with priority at most \c
382    /// p relative to \c Compare.
383    /// \param i The item.
384    /// \param p The priority.
385    void increase(const Item &i, const Prio &p) {
386      int idx = iim[i];
387      data[idx].prio = p;
388      bubble_up(idx);
389    }
390
391    /// \brief Returns if \c item is in, has already been in, or has
392    /// never been in the heap.
393    ///
394    /// This method returns PRE_HEAP if \c item has never been in the
395    /// heap, IN_HEAP if it is in the heap at the moment, and POST_HEAP
396    /// otherwise. In the latter case it is possible that \c item will
397    /// get back to the heap again.
398    /// \param i The item.
399    state_enum state(const Item &i) const {
400      int s = iim[i];
401      if( s >= 0 ) s = 0;
402      return state_enum(s);
403    }
404
405  }; // class RadixHeap
406
407
408  ///@}
409
410} // namespace lemon
411
412#endif // LEMON_RADIX_HEAP_H
Note: See TracBrowser for help on using the repository browser.