private static String toLispString(Tree<?> tree) { final String value = String.valueOf(tree.getValue()); if (tree.isLeaf()) { return value; } else { return String.format( "(%s %s)", value, tree.getChildren().map(Node::toLispString).mkString(" ")); } }
static <T> Stream<T> levelOrder(Tree<T> tree) { Stream<T> result = Stream.empty(); final java.util.Queue<Tree<T>> queue = new java.util.LinkedList<>(); queue.add(tree); while (!queue.isEmpty()) { final Tree<T> next = queue.remove(); result = result.prepend(next.getValue()); queue.addAll(next.getChildren().toJavaList()); } return result.reverse(); }
static <T> Stream<T> inOrder(Tree<T> tree) { if (tree.isLeaf()) { return Stream.of(tree.getValue()); } else { final List<Node<T>> children = tree.getChildren(); return children .tail() .foldLeft(Stream.<T>empty(), (acc, child) -> acc.appendAll(inOrder(child))) .prepend(tree.getValue()) .prependAll(inOrder(children.head())); } }
@SuppressWarnings("unchecked") static <T, U> Tree<U> apply( Node<T> node, Function<? super T, ? extends Iterable<? extends U>> mapper) { final Tree<U> mapped = Tree.ofAll(mapper.apply(node.getValue())); if (mapped.isEmpty()) { return Tree.empty(); } else { final List<Node<U>> children = (List<Node<U>>) (Object) node.getChildren() .map(child -> FlatMap.apply(child, mapper)) .filter(Tree::isDefined); return Tree.of(mapped.getValue(), children.prependAll(mapped.getChildren())); } }
static <T> Stream<T> postOrder(Tree<T> tree) { return tree.getChildren() .foldLeft(Stream.<T>empty(), (acc, child) -> acc.appendAll(postOrder(child))) .append(tree.getValue()); }
static <T> Stream<T> preOrder(Tree<T> tree) { return tree.getChildren() .foldLeft(Stream.of(tree.getValue()), (acc, child) -> acc.appendAll(preOrder(child))); }