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package bjc.utils.funcutils;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/** Various utility functions dealing with sets.
*
* @author bjculkin */
public class SetUtils {
/** Create a power-set (set of all subsets) of a given set.
*
* @param <T> The type of element in the set.
*
* @param originalSet The set to create a power-set of.
*
* @return The power-set of the set. */
public static <T> Set<Set<T>> powerSet(Set<T> originalSet) {
Set<Set<T>> sets = new HashSet<>();
// Special-case empty input
if (originalSet.isEmpty()) {
sets.add(new HashSet<T>());
return sets;
}
List<T> list = new ArrayList<>(originalSet);
// Add original set to list.
T head = list.get(0);
// Trim leading element from set.
Set<T> rest = new HashSet<>(list.subList(1, list.size()));
Set<Set<T>> remSets = powerSet(rest);
for (Set<T> set : remSets) {
Set<T> newSet = new HashSet<>();
// Create a new set with the removed element.
newSet.add(head);
newSet.addAll(set);
sets.add(newSet);
sets.add(set);
}
return sets;
}
/** Utility method for set construction.
*
* @param <T> The type of element in the set.
*
* @param elms The elements to stick in the set.
*
* @return A set containing the specified elements. */
@SafeVarargs
public static <T> Set<T> toSet(T... elms) {
Set<T> set = new HashSet<>();
for (T elm : elms) set.add(elm);
return set;
}
}
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