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copied!<p>I believe this is correct. It is not seeking efficiency, but a clean style through recursion and abstraction.</p> <p>The key abstraction is to introduce a simple <code>Tuple</code> class. This helps the generics later:</p> <pre><code>class Tuple<T> { private List<T> list = new ArrayList<T>(); public void add(T t) { list.add(t); } public void addAll(Tuple<T> subT) { for (T t : subT.list) { list.add(t); } } public String toString() { String result = "("; for (T t : list) { result += t + ", "; } result = result.substring(0, result.length() - 2); result += " )"; return result; } } </code></pre> <p>With this class, we can write a class like so:</p> <pre><code>public class Example { public static <T> List<Tuple<T>> cartesianProduct(List<Set<T>> sets) { List<Tuple<T>> tuples = new ArrayList<Tuple<T>>(); if (sets.size() == 1) { Set<T> set = sets.get(0); for (T t : set) { Tuple<T> tuple = new Tuple<T>(); tuple.add(t); tuples.add(tuple); } } else { Set<T> set = sets.remove(0); List<Tuple<T>> subTuples = cartesianProduct(sets); System.out.println("TRACER size = " + tuples.size()); for (Tuple<T> subTuple : subTuples) { for (T t : set) { Tuple<T> tuple = new Tuple<T>(); tuple.addAll(subTuple); tuple.add(t); tuples.add(tuple); } } } return tuples; } </code></pre> <p>}</p> <p>I have a decent example of this working, but it is omitted for brevity.</p>

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