com.google.common.collect.BinaryTreeTraverser.java Source code

Introduction

Here is the source code for com.google.common.collect.BinaryTreeTraverser.java

Source

/*
 * 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 com.google.common.collect;

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

import com.google.common.base.Optional;

import java.util.LinkedList;
import java.util.Iterator;

/**
 * A variant of {@link TreeTraverser} for binary trees, providing additional traversals specific to
 * binary trees.
 *
 * @author Louis Wasserman
 */
public abstract class BinaryTreeTraverser<T> extends TreeTraverser<T> {
    // TODO(lowasser): make this GWT-compatible when we've checked in ArrayDeque and BitSet emulation

    /**
     * Returns the left child of the specified node, or {@link Optional#absent()} if the specified
     * node has no left child.
     */
    public abstract Optional<T> leftChild(T root);

    /**
     * Returns the right child of the specified node, or {@link Optional#absent()} if the specified
     * node has no right child.
     */
    public abstract Optional<T> rightChild(T root);

    /**
     * Returns the children of this node, in left-to-right order.
     */
    @Override
    public final Iterable<T> children(final T root) {
        checkNotNull(root);
        return new FluentIterable<T>() {
            @Override
            public Iterator<T> iterator() {
                return new AbstractIterator<T>() {
                    boolean doneLeft;
                    boolean doneRight;

                    @Override
                    protected T computeNext() {
                        if (!doneLeft) {
                            doneLeft = true;
                            Optional<T> left = leftChild(root);
                            if (left.isPresent()) {
                                return left.get();
                            }
                        }
                        if (!doneRight) {
                            doneRight = true;
                            Optional<T> right = rightChild(root);
                            if (right.isPresent()) {
                                return right.get();
                            }
                        }
                        return endOfData();
                    }
                };
            }
        };
    }

    // TODO(lowasser): see if any significant optimizations are possible for breadthFirstIterator

    public final FluentIterable<T> inOrderTraversal(final T root) {
        checkNotNull(root);
        return new FluentIterable<T>() {
            @Override
            public UnmodifiableIterator<T> iterator() {
                return new InOrderIterator(root);
            }
        };
    }

    private static final class InOrderNode<T> {
        final T node;
        boolean hasExpandedLeft;

        InOrderNode(T node) {
            this.node = checkNotNull(node);
            this.hasExpandedLeft = false;
        }
    }

    private final class InOrderIterator extends AbstractIterator<T> {
        private final LinkedList<InOrderNode<T>> stack;

        InOrderIterator(T root) {
            this.stack = Lists.newLinkedList();
            stack.addLast(new InOrderNode<T>(root));
        }

        @Override
        protected T computeNext() {
            while (!stack.isEmpty()) {
                InOrderNode<T> inOrderNode = stack.getLast();
                if (inOrderNode.hasExpandedLeft) {
                    stack.removeLast();
                    pushIfPresent(rightChild(inOrderNode.node));
                    return inOrderNode.node;
                } else {
                    inOrderNode.hasExpandedLeft = true;
                    pushIfPresent(leftChild(inOrderNode.node));
                }
            }
            return endOfData();
        }

        private void pushIfPresent(Optional<T> node) {
            if (node.isPresent()) {
                stack.addLast(new InOrderNode<T>(node.get()));
            }
        }
    }
}