| /** |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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 org.apache.hadoop.util; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| |
| /** A PriorityQueue maintains a partial ordering of its elements such that the |
| least element can always be found in constant time. Put()'s and pop()'s |
| require log(size) time. */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Unstable |
| public abstract class PriorityQueue<T> { |
| private T[] heap; |
| private int size; |
| private int maxSize; |
| |
| /** Determines the ordering of objects in this priority queue. Subclasses |
| must define this one method. */ |
| protected abstract boolean lessThan(Object a, Object b); |
| |
| /** Subclass constructors must call this. */ |
| @SuppressWarnings("unchecked") |
| protected final void initialize(int maxSize) { |
| size = 0; |
| int heapSize = maxSize + 1; |
| heap = (T[]) new Object[heapSize]; |
| this.maxSize = maxSize; |
| } |
| |
| /** |
| * Adds an Object to a PriorityQueue in log(size) time. |
| * If one tries to add more objects than maxSize from initialize |
| * a RuntimeException (ArrayIndexOutOfBound) is thrown. |
| */ |
| public final void put(T element) { |
| size++; |
| heap[size] = element; |
| upHeap(); |
| } |
| |
| /** |
| * Adds element to the PriorityQueue in log(size) time if either |
| * the PriorityQueue is not full, or not lessThan(element, top()). |
| * @param element |
| * @return true if element is added, false otherwise. |
| */ |
| public boolean insert(T element){ |
| if (size < maxSize){ |
| put(element); |
| return true; |
| } |
| else if (size > 0 && !lessThan(element, top())){ |
| heap[1] = element; |
| adjustTop(); |
| return true; |
| } |
| else |
| return false; |
| } |
| |
| /** Returns the least element of the PriorityQueue in constant time. */ |
| public final T top() { |
| if (size > 0) |
| return heap[1]; |
| else |
| return null; |
| } |
| |
| /** Removes and returns the least element of the PriorityQueue in log(size) |
| time. */ |
| public final T pop() { |
| if (size > 0) { |
| T result = heap[1]; // save first value |
| heap[1] = heap[size]; // move last to first |
| heap[size] = null; // permit GC of objects |
| size--; |
| downHeap(); // adjust heap |
| return result; |
| } else |
| return null; |
| } |
| |
| /** Should be called when the Object at top changes values. Still log(n) |
| * worst case, but it's at least twice as fast to <pre> |
| * { pq.top().change(); pq.adjustTop(); } |
| * </pre> instead of <pre> |
| * { o = pq.pop(); o.change(); pq.push(o); } |
| * </pre> |
| */ |
| public final void adjustTop() { |
| downHeap(); |
| } |
| |
| |
| /** Returns the number of elements currently stored in the PriorityQueue. */ |
| public final int size() { |
| return size; |
| } |
| |
| /** Removes all entries from the PriorityQueue. */ |
| public final void clear() { |
| for (int i = 0; i <= size; i++) |
| heap[i] = null; |
| size = 0; |
| } |
| |
| private final void upHeap() { |
| int i = size; |
| T node = heap[i]; // save bottom node |
| int j = i >>> 1; |
| while (j > 0 && lessThan(node, heap[j])) { |
| heap[i] = heap[j]; // shift parents down |
| i = j; |
| j = j >>> 1; |
| } |
| heap[i] = node; // install saved node |
| } |
| |
| private final void downHeap() { |
| int i = 1; |
| T node = heap[i]; // save top node |
| int j = i << 1; // find smaller child |
| int k = j + 1; |
| if (k <= size && lessThan(heap[k], heap[j])) { |
| j = k; |
| } |
| while (j <= size && lessThan(heap[j], node)) { |
| heap[i] = heap[j]; // shift up child |
| i = j; |
| j = i << 1; |
| k = j + 1; |
| if (k <= size && lessThan(heap[k], heap[j])) { |
| j = k; |
| } |
| } |
| heap[i] = node; // install saved node |
| } |
| } |