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collection/lib/priority_queue.dart

Index: collection/lib/priority_queue.dart
diff --git a/collection/lib/priority_queue.dart b/collection/lib/priority_queue.dart
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-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-library dart.pkg.collection.priority_queue;
-
-import "dart:collection" show SplayTreeSet;
-
-/**
- * A priority queue is a priority based work-list of elements.
- *
- * The queue allows adding elements, and removing them again in priority order.
- */
-abstract class PriorityQueue<E> {
-  /**
-   * Number of elements in the queue.
-   */
-  int get length;
-
-  /**
-   * Whether the queue is empty.
-   */
-  bool get isEmpty;
-
-  /**
-   * Whether the queue has any elements.
-   */
-  bool get isNotEmpty;
-
-  /**
-   * Checks if [object] is in the queue.
-   *
-   * Returns true if the element is found.
-   */
-  bool contains(E object);
-
-  /**
-   * Adds element to the queue.
-   *
-   * The element will become the next to be removed by [removeFirst]
-   * when all elements with higher priority have been removed.
-   */
-  void add(E element);
-
-  /**
-   * Adds all [elements] to the queue.
-   */
-  void addAll(Iterable<E> elements);
-
-  /**
-   * Returns the next element that will be returned by [removeFirst].
-   *
-   * The element is not removed from the queue.
-   *
-   * The queue must not be empty when this method is called.
-   */
-  E get first;
-
-  /**
-   * Removes and returns the element with the highest priority.
-   *
-   * Repeatedly calling this method, without adding element in between,
-   * is guaranteed to return elements in non-decreasing order as, specified by
-   * [comparison].
-   *
-   * The queue must not be empty when this method is called.
-   */
-  E removeFirst();
-
-  /**
-   * Removes an element that compares equal to [element] in the queue.
-   *
-   * Returns true if an element is found and removed,
-   * and false if no equal element is found.
-   */
-  bool remove(E element);
-
-  /**
-   * Removes all the elements from this queue and returns them.
-   *
-   * The returned iterable has no specified order.
-   */
-  Iterable<E> removeAll();
-
-  /**
-   * Removes all the elements from this queue.
-   */
-  void clear();
-
-  /**
-   * Returns a list of the elements of this queue in priority order.
-   *
-   * The queue is not modified.
-   *
-   * The order is the order that the elements would be in if they were
-   * removed from this queue using [removeFirst].
-   */
-  List<E> toList();
-
-  /**
-   * Return a comparator based set using the comparator of this queue.
-   *
-   * The queue is not modified.
-   *
-   * The returned [Set] is currently a [SplayTreeSet],
-   * but this may change as other ordered sets are implemented.
-   *
-   * The set contains all the elements of this queue.
-   * If an element occurs more than once in the queue,
-   * the set will contain it only once.
-   */
-  Set<E> toSet();
-}
-
-/**
- * Heap based priority queue.
- *
- * The elements are kept in a heap structure,
- * where the element with the highest priority is immediately accessible,
- * and modifying a single element takes
- * logarithmic time in the number of elements on average.
- *
- * * The [add] and [removeFirst] operations take amortized logarithmic time,
- *   O(log(n)), but may occasionally take linear time when growing the capacity
- *   of the heap.
- * * The [addAll] operation works as doing repeated [add] operations.
- * * The [first] getter takes constant time, O(1).
- * * The [clear] and [removeAll] methods also take constant time, O(1).
- * * The [contains] and [remove] operations may need to search the entire
- *   queue for the elements, taking O(n) time.
- * * The [toList] operation effectively sorts the elements, taking O(n*log(n))
- *   time.
- * * The [toSet] operation effectively adds each element to the new set, taking
- *   an expected O(n*log(n)) time.
- */
-class HeapPriorityQueue<E> implements PriorityQueue<E> {
-  /**
-   * Initial capacity of a queue when created, or when added to after a [clear].
-   *
-   * Number can be any positive value. Picking a size that gives a whole
-   * number of "tree levels" in the heap is only done for aesthetic reasons.
-   */
-  static const int _INITIAL_CAPACITY = 7;
-
-  /**
-   * The comparison being used to compare the priority of elements.
-   */
-  final Comparator comparison;
-
-  /**
-   * List implementation of a heap.
-   */
-  List<E> _queue = new List<E>(_INITIAL_CAPACITY);
-
-  /**
-   * Number of elements in queue.
-   *
-   * The heap is implemented in the first [_length] entries of [_queue].
-   */
-  int _length = 0;
-
-  /**
-   * Create a new priority queue.
-   *
-   * The [comparison] is a [Comparator] used to compare the priority of
-   * elements. An element that compares as less than another element has
-   * a higher priority.
-   *
-   * If [comparison] is omitted, it defaults to [Comparable.compare].
-   */
-  HeapPriorityQueue([int comparison(E e1, E e2)])
-      : comparison = (comparison != null) ? comparison : Comparable.compare;
-
-  void add(E element) {
-    _add(element);
-  }
-
-  void addAll(Iterable<E> elements) {
-    for (E element in elements) {
-      _add(element);
-    }
-  }
-
-  void clear() {
-    _queue = const [];
-    _length = 0;
-  }
-
-  bool contains(E object) {
-    return _locate(object) >= 0;
-  }
-
-  E get first {
-    if (_length == 0) throw new StateError("No such element");
-    return _queue[0];
-  }
-
-  bool get isEmpty => _length == 0;
-
-  bool get isNotEmpty => _length != 0;
-
-  int get length => _length;
-
-  bool remove(E element) {
-    int index = _locate(element);
-    if (index < 0) return false;
-    E last = _removeLast();
-    if (index < _length) {
-      int comp = comparison(last, element);
-      if (comp <= 0) {
-        _bubbleUp(last, index);
-      } else {
-        _bubbleDown(last, index);
-      }
-    }
-    return true;
-  }
-
-  Iterable<E> removeAll() {
-    List<E> result = _queue;
-    int length = _length;
-    _queue = const [];
-    _length = 0;
-    return result.take(length);
-  }
-
-  E removeFirst() {
-    if (_length == 0) throw new StateError("No such element");
-    E result = _queue[0];
-    E last = _removeLast();
-    if (_length > 0) {
-      _bubbleDown(last, 0);
-    }
-    return result;
-  }
-
-  List<E> toList() {
-    List<E> list = new List<E>()..length = _length;
-    list.setRange(0, _length, _queue);
-    list.sort(comparison);
-    return list;
-  }
-
-  Set<E> toSet() {
-    Set<E> set = new SplayTreeSet<E>(comparison);
-    for (int i = 0; i < _length; i++) {
-      set.add(_queue[i]);
-    }
-    return set;
-  }
-
-  /**
-   * Returns some representation of the queue.
-   *
-   * The format isn't significant, and may change in the future.
-   */
-  String toString() {
-    return _queue.take(_length).toString();
-  }
-
-  /**
-   * Add element to the queue.
-   *
-   * Grows the capacity if the backing list is full.
-   */
-  void _add(E element) {
-    if (_length == _queue.length) _grow();
-    _bubbleUp(element, _length++);
-  }
-
-  /**
-   * Find the index of an object in the heap.
-   *
-   * Returns -1 if the object is not found.
-   */
-  int _locate(E object) {
-    if (_length == 0) return -1;
-    // Count positions from one instad of zero. This gives the numbers
-    // some nice properties. For example, all right children are odd,
-    // their left sibling is even, and the parent is found by shifting
-    // right by one.
-    // Valid range for position is [1.._length], inclusive.
-    int position = 1;
-    // Pre-order depth first search, omit child nodes if the current
-    // node has lower priority than [object], because all nodes lower
-    // in the heap will also have lower priority.
-    do {
-      int index = position - 1;
-      E element = _queue[index];
-      int comp = comparison(element, object);
-      if (comp == 0) return index;
-      if (comp < 0) {
-        // Element may be in subtree.
-        // Continue with the left child, if it is there.
-        int leftChildPosition = position * 2;
-        if (leftChildPosition <= _length) {
-          position = leftChildPosition;
-          continue;
-        }
-      }
-      // Find the next right sibling or right ancestor sibling.
-      do {
-        while (position.isOdd) {
-          // While position is a right child, go to the parent.
-          position >>= 1;
-        }
-        // Then go to the right sibling of the left-child.
-        position += 1;
-      } while (position > _length);  // Happens if last element is a left child.
-    } while (position != 1);  // At root again. Happens for right-most element.
-    return -1;
-  }
-
-  E _removeLast() {
-    int newLength = _length - 1;
-    E last = _queue[newLength];
-    _queue[newLength] = null;
-    _length = newLength;
-    return last;
-  }
-
-  /**
-   * Place [element] in heap at [index] or above.
-   *
-   * Put element into the empty cell at `index`.
-   * While the `element` has higher priority than the
-   * parent, swap it with the parent.
-   */
-  void _bubbleUp(E element, int index) {
-    while (index > 0) {
-      int parentIndex = (index - 1) ~/ 2;
-      E parent = _queue[parentIndex];
-      if (comparison(element, parent) > 0) break;
-      _queue[index] = parent;
-      index = parentIndex;
-    }
-    _queue[index] = element;
-  }
-
-  /**
-   * Place [element] in heap at [index] or above.
-   *
-   * Put element into the empty cell at `index`.
-   * While the `element` has lower priority than either child,
-   * swap it with the highest priority child.
-   */
-  void _bubbleDown(E element, int index) {
-    int rightChildIndex = index * 2 + 2;
-    while (rightChildIndex < _length) {
-      int leftChildIndex = rightChildIndex - 1;
-      E leftChild = _queue[leftChildIndex];
-      E rightChild = _queue[rightChildIndex];
-      int comp = comparison(leftChild, rightChild);
-      int minChildIndex;
-      E minChild;
-      if (comp < 0) {
-        minChild = leftChild;
-        minChildIndex = leftChildIndex;
-      } else {
-        minChild = rightChild;
-        minChildIndex = rightChildIndex;
-      }
-      comp = comparison(element, minChild);
-      if (comp <= 0) {
-        _queue[index] = element;
-        return;
-      }
-      _queue[index] = minChild;
-      index = minChildIndex;
-      rightChildIndex = index * 2 + 2;
-    }
-    int leftChildIndex = rightChildIndex - 1;
-    if (leftChildIndex < _length) {
-      E child = _queue[leftChildIndex];
-      int comp = comparison(element, child);
-      if (comp > 0) {
-        _queue[index] = child;
-        index = leftChildIndex;
-      }
-    }
-    _queue[index] = element;
-  }
-
-  /**
-   * Grows the capacity of the list holding the heap.
-   *
-   * Called when the list is full.
-   */
-  void _grow() {
-    int newCapacity = _queue.length * 2 + 1;
-    if (newCapacity < _INITIAL_CAPACITY) newCapacity = _INITIAL_CAPACITY;
-    List<E> newQueue = new List<E>(newCapacity);
-    newQueue.setRange(0, _length, _queue);
-    _queue = newQueue;
-  }
-}