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/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package jersey.repackaged.com.google.common.collect;

import static jersey.repackaged.com.google.common.base.Preconditions.checkNotNull;

import jersey.repackaged.com.google.common.annotations.Beta;
import jersey.repackaged.com.google.common.annotations.GwtCompatible;

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;
import java.util.Queue;

/**
 * Views elements of a type {@code T} as nodes in a tree, and provides methods to traverse the trees
 * induced by this traverser.
 *
 * 

For example, the tree * *

          {@code
 *          h
 *        / | \
 *       /  e  \
 *      d       g
 *     /|\      |
 *    / | \     f
 *   a  b  c       }
* *

can be iterated over in preorder (hdabcegf), postorder (abcdefgh), or breadth-first order * (hdegabcf). * *

Null nodes are strictly forbidden. * * @author Louis Wasserman * @since 15.0 */ @Beta @GwtCompatible(emulated = true) public abstract class TreeTraverser { // TODO(user): make this GWT-compatible when we've checked in ArrayDeque emulation /** * Returns the children of the specified node. Must not contain null. */ public abstract Iterable children(T root); /** * Returns an unmodifiable iterable over the nodes in a tree structure, using pre-order * traversal. That is, each node's subtrees are traversed after the node itself is returned. * *

No guarantees are made about the behavior of the traversal when nodes change while * iteration is in progress or when the iterators generated by {@link #children} are advanced. */ public final FluentIterable preOrderTraversal(final T root) { checkNotNull(root); return new FluentIterable() { @Override public UnmodifiableIterator iterator() { return preOrderIterator(root); } }; } // overridden in BinaryTreeTraverser UnmodifiableIterator preOrderIterator(T root) { return new PreOrderIterator(root); } private final class PreOrderIterator extends UnmodifiableIterator { private final Deque> stack; PreOrderIterator(T root) { this.stack = new ArrayDeque>(); stack.addLast(Iterators.singletonIterator(checkNotNull(root))); } @Override public boolean hasNext() { return !stack.isEmpty(); } @Override public T next() { Iterator itr = stack.getLast(); // throws NSEE if empty T result = checkNotNull(itr.next()); if (!itr.hasNext()) { stack.removeLast(); } Iterator childItr = children(result).iterator(); if (childItr.hasNext()) { stack.addLast(childItr); } return result; } } /** * Returns an unmodifiable iterable over the nodes in a tree structure, using post-order * traversal. That is, each node's subtrees are traversed before the node itself is returned. * *

No guarantees are made about the behavior of the traversal when nodes change while * iteration is in progress or when the iterators generated by {@link #children} are advanced. */ public final FluentIterable postOrderTraversal(final T root) { checkNotNull(root); return new FluentIterable() { @Override public UnmodifiableIterator iterator() { return postOrderIterator(root); } }; } // overridden in BinaryTreeTraverser UnmodifiableIterator postOrderIterator(T root) { return new PostOrderIterator(root); } private static final class PostOrderNode { final T root; final Iterator childIterator; PostOrderNode(T root, Iterator childIterator) { this.root = checkNotNull(root); this.childIterator = checkNotNull(childIterator); } } private final class PostOrderIterator extends AbstractIterator { private final ArrayDeque> stack; PostOrderIterator(T root) { this.stack = new ArrayDeque>(); stack.addLast(expand(root)); } @Override protected T computeNext() { while (!stack.isEmpty()) { PostOrderNode top = stack.getLast(); if (top.childIterator.hasNext()) { T child = top.childIterator.next(); stack.addLast(expand(child)); } else { stack.removeLast(); return top.root; } } return endOfData(); } private PostOrderNode expand(T t) { return new PostOrderNode(t, children(t).iterator()); } } /** * Returns an unmodifiable iterable over the nodes in a tree structure, using breadth-first * traversal. That is, all the nodes of depth 0 are returned, then depth 1, then 2, and so on. * *

No guarantees are made about the behavior of the traversal when nodes change while * iteration is in progress or when the iterators generated by {@link #children} are advanced. */ public final FluentIterable breadthFirstTraversal(final T root) { checkNotNull(root); return new FluentIterable() { @Override public UnmodifiableIterator iterator() { return new BreadthFirstIterator(root); } }; } private final class BreadthFirstIterator extends UnmodifiableIterator implements PeekingIterator { private final Queue queue; BreadthFirstIterator(T root) { this.queue = new ArrayDeque(); queue.add(root); } @Override public boolean hasNext() { return !queue.isEmpty(); } @Override public T peek() { return queue.element(); } @Override public T next() { T result = queue.remove(); Iterables.addAll(queue, children(result)); return result; } } }





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