55 lines
1.4 KiB
Rust
55 lines
1.4 KiB
Rust
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import option::none;
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import option::some;
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// A very naive implementation of union-find with unsigned integer nodes.
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// Maintains the invariant that the root of a node is always equal to or less
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// than the node itself.
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type node = option::t[uint];
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type ufind = rec(mutable node[mutable] nodes);
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fn make() -> ufind {
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ret rec(mutable nodes=~[mutable]);
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}
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fn make_set(&ufind ufnd) -> uint {
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auto idx = ivec::len(ufnd.nodes);
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ufnd.nodes += ~[mutable none[uint]];
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ret idx;
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}
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/// Creates sets as necessary to ensure that least `n` sets are present in the
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/// data structure.
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fn grow(&ufind ufnd, uint n) {
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while (set_count(ufnd) < n) { make_set(ufnd); }
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}
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fn find(&ufind ufnd, uint n) -> uint {
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alt (ufnd.nodes.(n)) {
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case (none) { ret n; }
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case (some(?m)) { auto m_ = m; be find(ufnd, m_); }
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}
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}
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fn union(&ufind ufnd, uint m, uint n) {
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auto m_root = find(ufnd, m);
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auto n_root = find(ufnd, n);
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if (m_root < n_root) {
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ufnd.nodes.(n_root) = some[uint](m_root);
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} else if (m_root > n_root) { ufnd.nodes.(m_root) = some[uint](n_root); }
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}
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fn set_count(&ufind ufnd) -> uint { ret ivec::len[node](ufnd.nodes); }
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// Removes all sets with IDs greater than or equal to the given value.
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fn prune(&ufind ufnd, uint n) {
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// TODO: Use "slice" once we get rid of "mutable?"
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auto len = ivec::len[node](ufnd.nodes);
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while (len != n) { ivec::pop[node](ufnd.nodes); len -= 1u; }
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}
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