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/*
* Copyright 2024 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef wasm_support_disjoint_sets_h
#define wasm_support_disjoint_sets_h
#include <cassert>
#include <cstddef>
#include <vector>
namespace wasm {
// A disjoint set forest (a.k.a. union-find) implementation. See
// https://en.wikipedia.org/wiki/Disjoint-set_data_structure.
struct DisjointSets {
struct ElemInfo {
// The index of the parent element, or the index of the element itself if it
// has no parent.
size_t parent;
// An upper bound on the height of the tree rooted at this element.
size_t rank;
};
std::vector<ElemInfo> info;
// Add an element and return its index.
size_t addSet() {
size_t ret = info.size();
info.push_back({ret, 0});
return ret;
}
// Get the representative element of the set to which `elem` belongs.
size_t getRoot(size_t elem) {
assert(elem < info.size());
size_t root = elem;
// Follow parent pointers up to the root.
for (; info[root].parent != root; root = info[root].parent) {
}
// Compress the path to make subsequent getRoots of this set faster.
while (elem != root) {
size_t parent = info[elem].parent;
info[elem].parent = root;
elem = parent;
}
return root;
}
// Join the sets to which the elements belong and return the representative
// element of the union.
size_t getUnion(size_t elem1, size_t elem2) {
assert(elem1 < info.size() && elem2 < info.size());
size_t root1 = getRoot(elem1);
size_t root2 = getRoot(elem2);
if (root1 == root2) {
// Already in the same set.
return root1;
}
// Canonicalize so that root1 has the greater rank.
if (info[root1].rank < info[root2].rank) {
std::swap(root1, root2);
}
// Merge the trees, smaller into larger.
info[root2].parent = root1;
// If the ranks were equal, the new root has a larger rank.
if (info[root1].rank == info[root2].rank) {
++info[root1].rank;
}
return root1;
}
};
} // namespace wasm
#endif // wasm_support_disjoint_sets_h
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