Mercurial > hg > orthanc-stone
comparison OrthancStone/Sources/Toolbox/DisjointDataSet.h @ 1512:244ad1e4e76a
reorganization of folders
author | Sebastien Jodogne <s.jodogne@gmail.com> |
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date | Tue, 07 Jul 2020 16:21:02 +0200 |
parents | Framework/Toolbox/DisjointDataSet.h@2d8ab34c8c91 |
children | 8563ea5d8ae4 |
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1511:9dfeee74c1e6 | 1512:244ad1e4e76a |
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1 /** | |
2 * Stone of Orthanc | |
3 * Copyright (C) 2012-2016 Sebastien Jodogne, Medical Physics | |
4 * Department, University Hospital of Liege, Belgium | |
5 * Copyright (C) 2017-2020 Osimis S.A., Belgium | |
6 * | |
7 * This program is free software: you can redistribute it and/or | |
8 * modify it under the terms of the GNU Affero General Public License | |
9 * as published by the Free Software Foundation, either version 3 of | |
10 * the License, or (at your option) any later version. | |
11 * | |
12 * This program is distributed in the hope that it will be useful, but | |
13 * WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 * Affero General Public License for more details. | |
16 * | |
17 * You should have received a copy of the GNU Affero General Public License | |
18 * along with this program. If not, see <http://www.gnu.org/licenses/>. | |
19 **/ | |
20 | |
21 #pragma once | |
22 | |
23 #include <vector> | |
24 | |
25 #include "../StoneException.h" | |
26 | |
27 namespace OrthancStone | |
28 { | |
29 class DisjointDataSet | |
30 { | |
31 public: | |
32 DisjointDataSet(size_t itemCount) : | |
33 parents_(itemCount), | |
34 ranks_(itemCount) | |
35 { | |
36 for (size_t index = 0; index < parents_.size(); index++) | |
37 { | |
38 SetParent(index,index); | |
39 ranks_[index] = 1; | |
40 } | |
41 } | |
42 | |
43 size_t Find(size_t item) | |
44 { | |
45 /* | |
46 If parents_[i] == i, it means i is representative of a set. | |
47 Otherwise, we go up the tree... | |
48 */ | |
49 if (GetParent(item) != item) | |
50 { | |
51 // if item is not a top item (representative of its set), | |
52 // we use path compression to improve future lookups | |
53 // see: https://en.wikipedia.org/wiki/Disjoint-set_data_structure#Path_compression | |
54 SetParent(item, Find(parents_[item])); | |
55 } | |
56 | |
57 // now that paths have been compressed, we are positively certain | |
58 // that item's parent is a set ("X is a set" means that X is the | |
59 // representative of a set) | |
60 return GetParent(item); | |
61 } | |
62 | |
63 /* | |
64 This merge the two sets that contains itemA and itemB | |
65 */ | |
66 void Union(size_t itemA, size_t itemB) | |
67 { | |
68 // Find current sets of x and y | |
69 size_t setA = Find(itemA); | |
70 size_t setB = Find(itemB); | |
71 | |
72 // if setA == setB, it means they are already in the same set and | |
73 // do not need to be merged! | |
74 if (setA != setB) | |
75 { | |
76 // we need to merge the sets, which means that the trees representing | |
77 // the sets needs to be merged (there must be a single top parent to | |
78 // all the items originally belonging to setA and setB must be the same) | |
79 | |
80 // since the algorithm speed is inversely proportional to the tree | |
81 // height (the rank), we need to combine trees in a way that | |
82 // minimizes this rank. See "Union by rank" at | |
83 // https://en.wikipedia.org/wiki/Disjoint-set_data_structure#by_rank | |
84 if (GetRank(setA) < GetRank(setB)) | |
85 { | |
86 SetParent(setA, setB); | |
87 } | |
88 else if (GetRank(setA) > GetRank(setB)) | |
89 { | |
90 SetParent(setB, setA); | |
91 } | |
92 else | |
93 { | |
94 SetParent(setB, setA); | |
95 BumpRank(setA); | |
96 // the trees had the same height but we attached the whole of setB | |
97 // under setA (under its parent), so the resulting tree is now | |
98 // 1 higher. setB is NOT representative of a set anymore. | |
99 } | |
100 } | |
101 } | |
102 | |
103 private: | |
104 size_t GetRank(size_t i) const | |
105 { | |
106 ORTHANC_ASSERT(i < ranks_.size()); | |
107 ORTHANC_ASSERT(ranks_.size() == parents_.size()); | |
108 return ranks_[i]; | |
109 } | |
110 | |
111 size_t GetParent(size_t i) const | |
112 { | |
113 ORTHANC_ASSERT(i < parents_.size()); | |
114 ORTHANC_ASSERT(ranks_.size() == parents_.size()); | |
115 return parents_[i]; | |
116 } | |
117 | |
118 void SetParent(size_t i, size_t parent) | |
119 { | |
120 ORTHANC_ASSERT(i < parents_.size()); | |
121 ORTHANC_ASSERT(ranks_.size() == parents_.size()); | |
122 parents_[i] = parent; | |
123 } | |
124 | |
125 void BumpRank(size_t i) | |
126 { | |
127 ORTHANC_ASSERT(i < ranks_.size()); | |
128 ORTHANC_ASSERT(ranks_.size() == parents_.size()); | |
129 ranks_[i] = ranks_[i] + 1u; | |
130 } | |
131 | |
132 /* | |
133 This vector contains the direct parent of each item | |
134 */ | |
135 std::vector<size_t> parents_; | |
136 | |
137 /* | |
138 This vector contains the tree height of each set. The values in the | |
139 vector for non-representative items is UNDEFINED! | |
140 */ | |
141 std::vector<size_t> ranks_; | |
142 }; | |
143 | |
144 } |