@SuppressWarnings("unchecked")
@Override
default Tuple2<Seq<T>, Seq<T>> span(Predicate<? super T> predicate) {
Objects.requireNonNull(predicate, "predicate is null");
if (isEmpty()) {
return Tuple.of(Stream.empty(), Stream.empty());
} else {
return (Tuple2<Seq<T>, Seq<T>>) traverse().span(predicate);
}
}
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()));
}
}
@Override
default Seq<T> takeRight(int n) {
if (isEmpty()) {
return Stream.empty();
} else {
return traverse().takeRight(n);
}
}
@Override
default Seq<T> dropRight(int n) {
if (n >= length()) {
return Stream.empty();
} else {
return traverse().dropRight(n);
}
}
@Override
default Seq<T> filter(Predicate<? super T> predicate) {
Objects.requireNonNull(predicate, "predicate is null");
if (isEmpty()) {
return Stream.empty();
} else {
return traverse().filter(predicate);
}
}
@Override
default <U> Seq<T> distinctBy(Function<? super T, ? extends U> keyExtractor) {
Objects.requireNonNull(keyExtractor, "keyExtractor is null");
if (isEmpty()) {
return Stream.empty();
} else {
return traverse().distinctBy(keyExtractor);
}
}
@Override
default Seq<T> distinctBy(Comparator<? super T> comparator) {
Objects.requireNonNull(comparator, "comparator is null");
if (isEmpty()) {
return Stream.empty();
} else {
return traverse().distinctBy(comparator);
}
}
/**
* Traverses the Tree in a specific order.
*
* @param order the tree traversal order
* @return A List containing all elements of this tree, which is List if this tree is empty.
* @throws java.lang.NullPointerException if order is null
*/
default Seq<T> traverse(Order order) {
Objects.requireNonNull(order, "order is null");
if (isEmpty()) {
return Stream.empty();
} else {
switch (order) {
case PRE_ORDER:
return Traversal.preOrder(this);
case IN_ORDER:
return Traversal.inOrder(this);
case POST_ORDER:
return Traversal.postOrder(this);
case LEVEL_ORDER:
return Traversal.levelOrder(this);
default:
throw new IllegalStateException("Unknown order: " + order.name());
}
}
}
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)));
}