94 lines
1.9 KiB
C++
94 lines
1.9 KiB
C++
/* SPDX-FileCopyrightText: 2023 Blender Authors
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*
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* SPDX-License-Identifier: GPL-2.0-or-later */
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#pragma once
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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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#include "BLI_index_range.hh"
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namespace blender {
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template<typename T = int64_t> class DisjointSet {
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private:
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Array<T> parents_;
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Array<T> 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(const int64_t size) : parents_(size), ranks_(size, 0)
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{
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BLI_assert(size >= 0);
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for (const int64_t i : IndexRange(size)) {
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parents_[i] = T(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(const T x, const T y)
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{
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T root1 = this->find_root(x);
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T 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(const T x, const T y)
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{
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T root1 = this->find_root(x);
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T 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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T find_root(const T x)
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{
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/* Find root by following parents. */
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T 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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T to_root = x;
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while (parents_[to_root] != root) {
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const T parent = parents_[to_root];
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parents_[to_root] = root;
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to_root = 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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