Add some additional utilities

This adds some list/set utilities, including an implementation of 'plain
changes' for generating list permutations that I suspect needs some
debugging.

1 files changed, 45 insertions, 0 deletions

diff --git a/base/src/main/java/bjc/utils/funcutils/SetUtils.java b/base/src/main/java/bjc/utils/funcutils/SetUtils.java
new file mode 100644
index 0000000..eac417c
--- /dev/null
+++ b/base/src/main/java/bjc/utils/funcutils/SetUtils.java
@@ -0,0 +1,45 @@
+package bjc.utils.funcutils;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public class SetUtils {
+	public static <T> Set<Set<T>> powerSet(Set<T> originalSet) {
+		Set<Set<T>> sets = new HashSet<Set<T>>();
+
+		if (originalSet.isEmpty()) {
+			sets.add(new HashSet<T>());
+			return sets;
+		}
+
+		List<T> list = new ArrayList<T>(originalSet);
+
+		T head = list.get(0);
+
+		Set<T> rest = new HashSet<T>(list.subList(1, list.size()));
+
+		for (Set<T> set : powerSet(rest)) {
+			Set<T> newSet = new HashSet<T>();
+
+			newSet.add(head);
+			newSet.addAll(set);
+
+			sets.add(newSet);
+			sets.add(set);
+		}
+
+		return sets;
+	}
+
+	public static <T> Set<T> toSet(T... elms) {
+		Set<T> set = new HashSet<>();
+
+		for(T elm : elms) {
+			set.add(elm);
+		}
+
+		return set;
+	}
+}