tasks a-s

Task/Power-set/Java/power-set-2.java

@@ -0,0 +1,23 @@
+public static <T> List<List<T>> powerset(Collection<T> list) {
+  List<List<T>> ps = new ArrayList<List<T>>();
+  ps.add(new ArrayList<T>());   // add the empty set
+
+  // for every item in the original list
+  for (T item : list) {
+    List<List<T>> newPs = new ArrayList<List<T>>();
+
+    for (List<T> subset : ps) {
+      // copy all of the current powerset's subsets
+      newPs.add(subset);
+
+      // plus the subsets appended with the current item
+      List<T> newSubset = new ArrayList<T>(subset);
+      newSubset.add(item);
+      newPs.add(newSubset);
+    }
+
+    // powerset is now powerset of list.subList(0, list.indexOf(item)+1)
+    ps = newPs;
+  }
+  return ps;
+}