106 lines
2.5 KiB
C++
106 lines
2.5 KiB
C++
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/*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#ifndef __BLI_DISJOINT_SET_HH__
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#define __BLI_DISJOINT_SET_HH__
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/** \file
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* \ingroup bli
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*
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* This implements the disjoint set data structure with path compression and union by rank.
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*/
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#include "BLI_array.hh"
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namespace blender {
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class DisjointSet {
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private:
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Array<uint> parents_;
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Array<uint> ranks_;
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public:
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/**
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* Create a new disjoint set with the given size. Initially, every element is in a separate set.
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*/
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DisjointSet(uint size) : parents_(size), ranks_(size, 0)
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{
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for (uint i = 0; i < size; i++) {
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parents_[i] = i;
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}
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}
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/**
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* Join the sets containing elements x and y. Nothing happens when they have been in the same set
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* before.
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*/
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void join(uint x, uint y)
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{
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uint root1 = this->find_root(x);
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uint root2 = this->find_root(y);
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/* x and y are in the same set already. */
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if (root1 == root2) {
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return;
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}
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/* Implement union by rank heuristic. */
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if (ranks_[root1] < ranks_[root2]) {
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std::swap(root1, root2);
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}
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parents_[root2] = root1;
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if (ranks_[root1] == ranks_[root2]) {
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ranks_[root1]++;
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}
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}
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/**
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* Return true when x and y are in the same set.
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*/
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bool in_same_set(uint x, uint y)
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{
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uint root1 = this->find_root(x);
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uint root2 = this->find_root(y);
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return root1 == root2;
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}
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/**
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* Find the element that represents the set containing x currently.
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*/
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uint find_root(uint x)
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{
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/* Find root by following parents. */
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uint root = x;
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while (parents_[root] != root) {
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root = parents_[root];
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}
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/* Compress path. */
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while (parents_[x] != root) {
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uint parent = parents_[x];
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parents_[x] = root;
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x = parent;
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}
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return root;
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}
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};
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} // namespace blender
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#endif /* __BLI_DISJOINT_SET_HH__ */
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