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stdlib: Modify union-find to guarantee that root nodes are always less than or equal to leaf nodes; add a "prune" method

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This commit is contained in:
Patrick Walton 2011-05-20 15:46:01 -07:00
parent 36c083b14c
commit 4eb476fc75
1 changed files with 18 additions and 7 deletions
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25
src/lib/ufind.rs
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@ -2,6 +2,8 @@ import option::none;
import option::some;
// A very naive implementation of union-find with unsigned integer nodes.
// Maintains the invariant that the root of a node is always equal to or less
// than the node itself.
type node = option::t[uint];
type ufind = rec(mutable vec[mutable node] nodes);
@ -20,18 +22,27 @@ fn make_set(&ufind ufnd) -> uint {
fn find(&ufind ufnd, uint n) -> uint {
alt (ufnd.nodes.(n)) {
case (none[uint]) { ret n; }
case (some[uint](?m)) {
// TODO: "be"
ret find(ufnd, m);
}
case (none[uint]) { ret n; }
case (some[uint](?m)) { be find(ufnd, m); }
}
}
fn union(&ufind ufnd, uint m, uint n) {
auto m_root = find(ufnd, m);
auto n_root = find(ufnd, n);
auto ptr = some[uint](n_root);
ufnd.nodes.(m_root) = ptr;
if (m_root < n_root) {
ufnd.nodes.(n_root) = some[uint](m_root);
} else {
ufnd.nodes.(m_root) = some[uint](n_root);
}
}
// Removes all sets with IDs greater than or equal to the given value.
fn prune(&ufind ufnd, uint n) {
// TODO: Use "slice" once we get rid of "mutable?"
while (n != 0u) {
vec::pop[node](ufnd.nodes);
n -= 1u;
}
}