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#include "union_find.hpp"
#include "utils.hpp"
#include <algorithm>
#include <cassert>
namespace terraces {
union_find::union_find(index n, utils::stack_allocator<index> a) : m_parent(n, n, a) {
#ifndef NDEBUG
m_compressed = true;
#endif // NDEBUG
}
index union_find::find(index x) {
assert(x < m_parent.size());
index root = x;
while (!is_representative(root)) {
root = m_parent[root];
}
while (x != root) {
x = utils::exchange(m_parent[x], root);
}
assert(is_representative(root) && root < m_parent.size());
return root;
}
void union_find::compress() {
for (index i = 0; i < m_parent.size(); ++i) {
find(i);
}
#ifndef NDEBUG
m_compressed = true;
#endif // NDEBUG
}
void union_find::merge(index x, index y) {
#ifndef NDEBUG
m_compressed = false;
#endif // NDEBUG
index i = find(x);
index j = find(y);
if (i == j) {
return;
}
if (m_parent[i] < m_parent[j]) {
// link the smaller group to the larger one
m_parent[i] = j;
} else if (m_parent[i] > m_parent[j]) {
// link the smaller group to the larger one
m_parent[j] = i;
} else {
// equal rank: link arbitrarily and increase rank
m_parent[j] = i;
++m_parent[i];
}
}
union_find union_find::make_bipartition(const std::vector<bool>& split,
utils::stack_allocator<index> alloc) {
union_find result(split.size(), alloc);
std::array<index, 2> fst{{none, none}};
for (index i = 0; i < split.size(); ++i) {
auto& repr = fst[split[i]];
repr = repr == none ? i : repr;
result.merge(repr, i);
}
result.compress();
return result;
}
} // namespace terraces
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