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GenericPriorityQueue.cs
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GenericPriorityQueue.cs
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using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
namespace Priority_Queue
{
/// <summary>
/// A copy of StablePriorityQueue which also has generic priority-type
/// </summary>
/// <typeparam name="TItem">The values in the queue. Must extend the GenericPriorityQueueNode class</typeparam>
/// <typeparam name="TPriority">The priority-type. Must extend IComparable<TPriority></typeparam>
public sealed class GenericPriorityQueue<TItem, TPriority> : IFixedSizePriorityQueue<TItem, TPriority>
where TItem : GenericPriorityQueueNode<TPriority>
{
private int _numNodes;
private TItem[] _nodes;
private long _numNodesEverEnqueued;
private readonly Comparison<TPriority> _comparer;
/// <summary>
/// Instantiate a new Priority Queue
/// </summary>
/// <param name="maxNodes">The max nodes ever allowed to be enqueued (going over this will cause undefined behavior)</param>
public GenericPriorityQueue(int maxNodes) : this(maxNodes, Comparer<TPriority>.Default) { }
/// <summary>
/// Instantiate a new Priority Queue
/// </summary>
/// <param name="maxNodes">The max nodes ever allowed to be enqueued (going over this will cause undefined behavior)</param>
/// <param name="comparer">The comparer used to compare TPriority values.</param>
public GenericPriorityQueue(int maxNodes, IComparer<TPriority> comparer) : this(maxNodes, comparer.Compare) { }
/// <summary>
/// Instantiate a new Priority Queue
/// </summary>
/// <param name="maxNodes">The max nodes ever allowed to be enqueued (going over this will cause undefined behavior)</param>
/// <param name="comparer">The comparison function to use to compare TPriority values</param>
public GenericPriorityQueue(int maxNodes, Comparison<TPriority> comparer)
{
#if DEBUG
if (maxNodes <= 0)
{
throw new InvalidOperationException("New queue size cannot be smaller than 1");
}
#endif
_numNodes = 0;
_nodes = new TItem[maxNodes + 1];
_numNodesEverEnqueued = 0;
_comparer = comparer;
}
/// <summary>
/// Returns the number of nodes in the queue.
/// O(1)
/// </summary>
public int Count
{
get
{
return _numNodes;
}
}
/// <summary>
/// Returns the maximum number of items that can be enqueued at once in this queue. Once you hit this number (ie. once Count == MaxSize),
/// attempting to enqueue another item will cause undefined behavior. O(1)
/// </summary>
public int MaxSize
{
get
{
return _nodes.Length - 1;
}
}
/// <summary>
/// Removes every node from the queue.
/// O(n) (So, don't do this often!)
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public void Clear()
{
Array.Clear(_nodes, 1, _numNodes);
_numNodes = 0;
}
/// <summary>
/// Returns (in O(1)!) whether the given node is in the queue.
/// If node is or has been previously added to another queue, the result is undefined unless oldQueue.ResetNode(node) has been called
/// O(1)
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public bool Contains(TItem node)
{
#if DEBUG
if(node == null)
{
throw new ArgumentNullException("node");
}
if (node.Queue != null && !Equals(node.Queue))
{
throw new InvalidOperationException("node.Contains was called on a node from another queue. Please call originalQueue.ResetNode() first");
}
if (node.QueueIndex < 0 || node.QueueIndex >= _nodes.Length)
{
throw new InvalidOperationException("node.QueueIndex has been corrupted. Did you change it manually?");
}
#endif
return (_nodes[node.QueueIndex] == node);
}
/// <summary>
/// Enqueue a node to the priority queue. Lower values are placed in front. Ties are broken by first-in-first-out.
/// If the queue is full, the result is undefined.
/// If the node is already enqueued, the result is undefined.
/// If node is or has been previously added to another queue, the result is undefined unless oldQueue.ResetNode(node) has been called
/// O(log n)
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public void Enqueue(TItem node, TPriority priority)
{
#if DEBUG
if(node == null)
{
throw new ArgumentNullException("node");
}
if(_numNodes >= _nodes.Length - 1)
{
throw new InvalidOperationException("Queue is full - node cannot be added: " + node);
}
if (node.Queue != null && !Equals(node.Queue))
{
throw new InvalidOperationException("node.Enqueue was called on a node from another queue. Please call originalQueue.ResetNode() first");
}
if (Contains(node))
{
throw new InvalidOperationException("Node is already enqueued: " + node);
}
node.Queue = this;
#endif
node.Priority = priority;
_numNodes++;
_nodes[_numNodes] = node;
node.QueueIndex = _numNodes;
node.InsertionIndex = _numNodesEverEnqueued++;
CascadeUp(node);
}
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
private void CascadeUp(TItem node)
{
//aka Heapify-up
int parent;
if (node.QueueIndex > 1)
{
parent = node.QueueIndex >> 1;
TItem parentNode = _nodes[parent];
if(HasHigherPriority(parentNode, node))
return;
//Node has lower priority value, so move parent down the heap to make room
_nodes[node.QueueIndex] = parentNode;
parentNode.QueueIndex = node.QueueIndex;
node.QueueIndex = parent;
}
else
{
return;
}
while(parent > 1)
{
parent >>= 1;
TItem parentNode = _nodes[parent];
if(HasHigherPriority(parentNode, node))
break;
//Node has lower priority value, so move parent down the heap to make room
_nodes[node.QueueIndex] = parentNode;
parentNode.QueueIndex = node.QueueIndex;
node.QueueIndex = parent;
}
_nodes[node.QueueIndex] = node;
}
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
private void CascadeDown(TItem node)
{
//aka Heapify-down
int finalQueueIndex = node.QueueIndex;
int childLeftIndex = 2 * finalQueueIndex;
// If leaf node, we're done
if(childLeftIndex > _numNodes)
{
return;
}
// Check if the left-child is higher-priority than the current node
int childRightIndex = childLeftIndex + 1;
TItem childLeft = _nodes[childLeftIndex];
if(HasHigherPriority(childLeft, node))
{
// Check if there is a right child. If not, swap and finish.
if(childRightIndex > _numNodes)
{
node.QueueIndex = childLeftIndex;
childLeft.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childLeft;
_nodes[childLeftIndex] = node;
return;
}
// Check if the left-child is higher-priority than the right-child
TItem childRight = _nodes[childRightIndex];
if(HasHigherPriority(childLeft, childRight))
{
// left is highest, move it up and continue
childLeft.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childLeft;
finalQueueIndex = childLeftIndex;
}
else
{
// right is even higher, move it up and continue
childRight.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childRight;
finalQueueIndex = childRightIndex;
}
}
// Not swapping with left-child, does right-child exist?
else if(childRightIndex > _numNodes)
{
return;
}
else
{
// Check if the right-child is higher-priority than the current node
TItem childRight = _nodes[childRightIndex];
if(HasHigherPriority(childRight, node))
{
childRight.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childRight;
finalQueueIndex = childRightIndex;
}
// Neither child is higher-priority than current, so finish and stop.
else
{
return;
}
}
while(true)
{
childLeftIndex = 2 * finalQueueIndex;
// If leaf node, we're done
if(childLeftIndex > _numNodes)
{
node.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = node;
break;
}
// Check if the left-child is higher-priority than the current node
childRightIndex = childLeftIndex + 1;
childLeft = _nodes[childLeftIndex];
if(HasHigherPriority(childLeft, node))
{
// Check if there is a right child. If not, swap and finish.
if(childRightIndex > _numNodes)
{
node.QueueIndex = childLeftIndex;
childLeft.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childLeft;
_nodes[childLeftIndex] = node;
break;
}
// Check if the left-child is higher-priority than the right-child
TItem childRight = _nodes[childRightIndex];
if(HasHigherPriority(childLeft, childRight))
{
// left is highest, move it up and continue
childLeft.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childLeft;
finalQueueIndex = childLeftIndex;
}
else
{
// right is even higher, move it up and continue
childRight.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childRight;
finalQueueIndex = childRightIndex;
}
}
// Not swapping with left-child, does right-child exist?
else if(childRightIndex > _numNodes)
{
node.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = node;
break;
}
else
{
// Check if the right-child is higher-priority than the current node
TItem childRight = _nodes[childRightIndex];
if(HasHigherPriority(childRight, node))
{
childRight.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = childRight;
finalQueueIndex = childRightIndex;
}
// Neither child is higher-priority than current, so finish and stop.
else
{
node.QueueIndex = finalQueueIndex;
_nodes[finalQueueIndex] = node;
break;
}
}
}
}
/// <summary>
/// Returns true if 'higher' has higher priority than 'lower', false otherwise.
/// Note that calling HasHigherPriority(node, node) (ie. both arguments the same node) will return false
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
private bool HasHigherPriority(TItem higher, TItem lower)
{
var cmp = _comparer(higher.Priority, lower.Priority);
return (cmp < 0 || (cmp == 0 && higher.InsertionIndex < lower.InsertionIndex));
}
/// <summary>
/// Removes the head of the queue (node with minimum priority; ties are broken by order of insertion), and returns it.
/// If queue is empty, result is undefined
/// O(log n)
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public TItem Dequeue()
{
#if DEBUG
if(_numNodes <= 0)
{
throw new InvalidOperationException("Cannot call Dequeue() on an empty queue");
}
if(!IsValidQueue())
{
throw new InvalidOperationException("Queue has been corrupted (Did you update a node priority manually instead of calling UpdatePriority()?" +
"Or add the same node to two different queues?)");
}
#endif
TItem returnMe = _nodes[1];
//If the node is already the last node, we can remove it immediately
if(_numNodes == 1)
{
_nodes[1] = null;
_numNodes = 0;
return returnMe;
}
//Swap the node with the last node
TItem formerLastNode = _nodes[_numNodes];
_nodes[1] = formerLastNode;
formerLastNode.QueueIndex = 1;
_nodes[_numNodes] = null;
_numNodes--;
//Now bubble formerLastNode (which is no longer the last node) down
CascadeDown(formerLastNode);
return returnMe;
}
/// <summary>
/// Resize the queue so it can accept more nodes. All currently enqueued nodes are remain.
/// Attempting to decrease the queue size to a size too small to hold the existing nodes results in undefined behavior
/// O(n)
/// </summary>
public void Resize(int maxNodes)
{
#if DEBUG
if (maxNodes <= 0)
{
throw new InvalidOperationException("Queue size cannot be smaller than 1");
}
if (maxNodes < _numNodes)
{
throw new InvalidOperationException("Called Resize(" + maxNodes + "), but current queue contains " + _numNodes + " nodes");
}
#endif
TItem[] newArray = new TItem[maxNodes + 1];
int highestIndexToCopy = Math.Min(maxNodes, _numNodes);
Array.Copy(_nodes, newArray, highestIndexToCopy + 1);
_nodes = newArray;
}
/// <summary>
/// Returns the head of the queue, without removing it (use Dequeue() for that).
/// If the queue is empty, behavior is undefined.
/// O(1)
/// </summary>
public TItem First
{
get
{
#if DEBUG
if(_numNodes <= 0)
{
throw new InvalidOperationException("Cannot call .First on an empty queue");
}
#endif
return _nodes[1];
}
}
/// <summary>
/// This method must be called on a node every time its priority changes while it is in the queue.
/// <b>Forgetting to call this method will result in a corrupted queue!</b>
/// Calling this method on a node not in the queue results in undefined behavior
/// O(log n)
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public void UpdatePriority(TItem node, TPriority priority)
{
#if DEBUG
if(node == null)
{
throw new ArgumentNullException("node");
}
if (node.Queue != null && !Equals(node.Queue))
{
throw new InvalidOperationException("node.UpdatePriority was called on a node from another queue");
}
if (!Contains(node))
{
throw new InvalidOperationException("Cannot call UpdatePriority() on a node which is not enqueued: " + node);
}
#endif
node.Priority = priority;
OnNodeUpdated(node);
}
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
private void OnNodeUpdated(TItem node)
{
//Bubble the updated node up or down as appropriate
int parentIndex = node.QueueIndex >> 1;
if(parentIndex > 0 && HasHigherPriority(node, _nodes[parentIndex]))
{
CascadeUp(node);
}
else
{
//Note that CascadeDown will be called if parentNode == node (that is, node is the root)
CascadeDown(node);
}
}
/// <summary>
/// Removes a node from the queue. The node does not need to be the head of the queue.
/// If the node is not in the queue, the result is undefined. If unsure, check Contains() first
/// O(log n)
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public void Remove(TItem node)
{
#if DEBUG
if(node == null)
{
throw new ArgumentNullException("node");
}
if (node.Queue != null && !Equals(node.Queue))
{
throw new InvalidOperationException("node.Remove was called on a node from another queue");
}
if (!Contains(node))
{
throw new InvalidOperationException("Cannot call Remove() on a node which is not enqueued: " + node);
}
#endif
//If the node is already the last node, we can remove it immediately
if(node.QueueIndex == _numNodes)
{
_nodes[_numNodes] = null;
_numNodes--;
return;
}
//Swap the node with the last node
TItem formerLastNode = _nodes[_numNodes];
_nodes[node.QueueIndex] = formerLastNode;
formerLastNode.QueueIndex = node.QueueIndex;
_nodes[_numNodes] = null;
_numNodes--;
//Now bubble formerLastNode (which is no longer the last node) up or down as appropriate
OnNodeUpdated(formerLastNode);
}
/// <summary>
/// By default, nodes that have been previously added to one queue cannot be added to another queue.
/// If you need to do this, please call originalQueue.ResetNode(node) before attempting to add it in the new queue
/// </summary>
#if NET_VERSION_4_5
[MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
public void ResetNode(TItem node)
{
#if DEBUG
if (node == null)
{
throw new ArgumentNullException("node");
}
if (node.Queue != null && !Equals(node.Queue))
{
throw new InvalidOperationException("node.ResetNode was called on a node from another queue");
}
if (Contains(node))
{
throw new InvalidOperationException("node.ResetNode was called on a node that is still in the queue");
}
node.Queue = null;
#endif
node.QueueIndex = 0;
}
public IEnumerator<TItem> GetEnumerator()
{
#if NET_VERSION_4_5 // ArraySegment does not implement IEnumerable before 4.5
IEnumerable<TItem> e = new ArraySegment<TItem>(_nodes, 1, _numNodes);
return e.GetEnumerator();
#else
for(int i = 1; i <= _numNodes; i++)
yield return _nodes[i];
#endif
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
/// <summary>
/// <b>Should not be called in production code.</b>
/// Checks to make sure the queue is still in a valid state. Used for testing/debugging the queue.
/// </summary>
public bool IsValidQueue()
{
for(int i = 1; i < _nodes.Length; i++)
{
if(_nodes[i] != null)
{
int childLeftIndex = 2 * i;
if(childLeftIndex < _nodes.Length && _nodes[childLeftIndex] != null && HasHigherPriority(_nodes[childLeftIndex], _nodes[i]))
return false;
int childRightIndex = childLeftIndex + 1;
if(childRightIndex < _nodes.Length && _nodes[childRightIndex] != null && HasHigherPriority(_nodes[childRightIndex], _nodes[i]))
return false;
}
}
return true;
}
}
}