Update #0 - First Release

sources/main/java/com/google/common/collect/BinaryTreeTraverser.java

@@ -0,0 +1,213 @@
+/*
+ * 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 java.util.ArrayDeque;
+import java.util.BitSet;
+import java.util.Deque;
+import java.util.Iterator;
+
+import com.google.common.annotations.Beta;
+import com.google.common.annotations.GwtCompatible;
+import com.google.common.base.Optional;
+
+/**
+ * A variant of {@link TreeTraverser} for binary trees, providing additional
+ * traversals specific to binary trees.
+ *
+ * @author Louis Wasserman
+ * @since 15.0
+ */
+@Beta
+@GwtCompatible(emulated = true)
+public abstract class BinaryTreeTraverser<T> extends TreeTraverser<T> {
+	// TODO(user): 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();
+					}
+				};
+			}
+		};
+	}
+
+	@Override
+	UnmodifiableIterator<T> preOrderIterator(T root) {
+		return new PreOrderIterator(root);
+	}
+
+	/*
+	 * Optimized implementation of preOrderIterator for binary trees.
+	 */
+	private final class PreOrderIterator extends UnmodifiableIterator<T> implements PeekingIterator<T> {
+		private final Deque<T> stack;
+
+		PreOrderIterator(T root) {
+			this.stack = new ArrayDeque<T>();
+			stack.addLast(root);
+		}
+
+		@Override
+		public boolean hasNext() {
+			return !stack.isEmpty();
+		}
+
+		@Override
+		public T next() {
+			T result = stack.removeLast();
+			pushIfPresent(stack, rightChild(result));
+			pushIfPresent(stack, leftChild(result));
+			return result;
+		}
+
+		@Override
+		public T peek() {
+			return stack.getLast();
+		}
+	}
+
+	@Override
+	UnmodifiableIterator<T> postOrderIterator(T root) {
+		return new PostOrderIterator(root);
+	}
+
+	/*
+	 * Optimized implementation of postOrderIterator for binary trees.
+	 */
+	private final class PostOrderIterator extends UnmodifiableIterator<T> {
+		private final Deque<T> stack;
+		private final BitSet hasExpanded;
+
+		PostOrderIterator(T root) {
+			this.stack = new ArrayDeque<T>();
+			stack.addLast(root);
+			this.hasExpanded = new BitSet();
+		}
+
+		@Override
+		public boolean hasNext() {
+			return !stack.isEmpty();
+		}
+
+		@Override
+		public T next() {
+			while (true) {
+				T node = stack.getLast();
+				boolean expandedNode = hasExpanded.get(stack.size() - 1);
+				if (expandedNode) {
+					stack.removeLast();
+					hasExpanded.clear(stack.size());
+					return node;
+				} else {
+					hasExpanded.set(stack.size() - 1);
+					pushIfPresent(stack, rightChild(node));
+					pushIfPresent(stack, leftChild(node));
+				}
+			}
+		}
+	}
+
+	// TODO(user): 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 final class InOrderIterator extends AbstractIterator<T> {
+		private final Deque<T> stack;
+		private final BitSet hasExpandedLeft;
+
+		InOrderIterator(T root) {
+			this.stack = new ArrayDeque<T>();
+			this.hasExpandedLeft = new BitSet();
+			stack.addLast(root);
+		}
+
+		@Override
+		protected T computeNext() {
+			while (!stack.isEmpty()) {
+				T node = stack.getLast();
+				if (hasExpandedLeft.get(stack.size() - 1)) {
+					stack.removeLast();
+					hasExpandedLeft.clear(stack.size());
+					pushIfPresent(stack, rightChild(node));
+					return node;
+				} else {
+					hasExpandedLeft.set(stack.size() - 1);
+					pushIfPresent(stack, leftChild(node));
+				}
+			}
+			return endOfData();
+		}
+	}
+
+	private static <T> void pushIfPresent(Deque<T> stack, Optional<T> node) {
+		if (node.isPresent()) {
+			stack.addLast(node.get());
+		}
+	}
+}