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comparison OrthancStone/Resources/Graveyard/RTStructTentativeReimplementation-BGO/DisjointDataSet.h @ 1908:affde38b84de

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moved tentative bgo reimplementation of rt-struct into graveyard
author Sebastien Jodogne <s.jodogne@gmail.com>
date Tue, 01 Feb 2022 08:38:32 +0100
parents OrthancStone/Sources/Toolbox/DisjointDataSet.h@7053b8a0aaec
children 07964689cb0b
comparison
equal deleted inserted replaced
1907:0208f99b8bde 1908:affde38b84de
1 /**
2 * Stone of Orthanc
3 * Copyright (C) 2012-2016 Sebastien Jodogne, Medical Physics
4 * Department, University Hospital of Liege, Belgium
5 * Copyright (C) 2017-2022 Osimis S.A., Belgium
6 * Copyright (C) 2021-2022 Sebastien Jodogne, ICTEAM UCLouvain, Belgium
7 *
8 * This program is free software: you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public License
10 * as published by the Free Software Foundation, either version 3 of
11 * the License, or (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this program. If not, see
20 * <http://www.gnu.org/licenses/>.
21 **/
22
23 #pragma once
24
25 #include <vector>
26
27 #include "../StoneException.h"
28
29 namespace OrthancStone
30 {
31 class DisjointDataSet
32 {
33 public:
34 DisjointDataSet(size_t itemCount) :
35 parents_(itemCount),
36 ranks_(itemCount)
37 {
38 for (size_t index = 0; index < parents_.size(); index++)
39 {
40 SetParent(index,index);
41 ranks_[index] = 1;
42 }
43 }
44
45 size_t Find(size_t item)
46 {
47 /*
48 If parents_[i] == i, it means i is representative of a set.
49 Otherwise, we go up the tree...
50 */
51 if (GetParent(item) != item)
52 {
53 // if item is not a top item (representative of its set),
54 // we use path compression to improve future lookups
55 // see: https://en.wikipedia.org/wiki/Disjoint-set_data_structure#Path_compression
56 SetParent(item, Find(parents_[item]));
57 }
58
59 // now that paths have been compressed, we are positively certain
60 // that item's parent is a set ("X is a set" means that X is the
61 // representative of a set)
62 return GetParent(item);
63 }
64
65 /*
66 This merge the two sets that contains itemA and itemB
67 */
68 void Union(size_t itemA, size_t itemB)
69 {
70 // Find current sets of x and y
71 size_t setA = Find(itemA);
72 size_t setB = Find(itemB);
73
74 // if setA == setB, it means they are already in the same set and
75 // do not need to be merged!
76 if (setA != setB)
77 {
78 // we need to merge the sets, which means that the trees representing
79 // the sets needs to be merged (there must be a single top parent to
80 // all the items originally belonging to setA and setB must be the same)
81
82 // since the algorithm speed is inversely proportional to the tree
83 // height (the rank), we need to combine trees in a way that
84 // minimizes this rank. See "Union by rank" at
85 // https://en.wikipedia.org/wiki/Disjoint-set_data_structure#by_rank
86 if (GetRank(setA) < GetRank(setB))
87 {
88 SetParent(setA, setB);
89 }
90 else if (GetRank(setA) > GetRank(setB))
91 {
92 SetParent(setB, setA);
93 }
94 else
95 {
96 SetParent(setB, setA);
97 BumpRank(setA);
98 // the trees had the same height but we attached the whole of setB
99 // under setA (under its parent), so the resulting tree is now
100 // 1 higher. setB is NOT representative of a set anymore.
101 }
102 }
103 }
104
105 private:
106 size_t GetRank(size_t i) const
107 {
108 ORTHANC_ASSERT(i < ranks_.size());
109 ORTHANC_ASSERT(ranks_.size() == parents_.size());
110 return ranks_[i];
111 }
112
113 size_t GetParent(size_t i) const
114 {
115 ORTHANC_ASSERT(i < parents_.size());
116 ORTHANC_ASSERT(ranks_.size() == parents_.size());
117 return parents_[i];
118 }
119
120 void SetParent(size_t i, size_t parent)
121 {
122 ORTHANC_ASSERT(i < parents_.size());
123 ORTHANC_ASSERT(ranks_.size() == parents_.size());
124 parents_[i] = parent;
125 }
126
127 void BumpRank(size_t i)
128 {
129 ORTHANC_ASSERT(i < ranks_.size());
130 ORTHANC_ASSERT(ranks_.size() == parents_.size());
131 ranks_[i] = ranks_[i] + 1u;
132 }
133
134 /*
135 This vector contains the direct parent of each item
136 */
137 std::vector<size_t> parents_;
138
139 /*
140 This vector contains the tree height of each set. The values in the
141 vector for non-representative items is UNDEFINED!
142 */
143 std::vector<size_t> ranks_;
144 };
145
146 }