/* -*- tab-width: 4 -*-
*
* Electric(tm) VLSI Design System
*
* File: AStar.java
* Written by: Christian Harnisch, Ingo Besenfelder, Michael Neumann (Team 3)
*
* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
*
* Electric(tm) is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* Electric(tm) is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Electric(tm); see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, Mass 02111-1307, USA.
*/
package com.sun.electric.tool.routing.experimentalAStar2.algorithm;
import java.util.LinkedList;
import java.util.List;
import com.sun.electric.tool.routing.experimentalAStar2.memorymanager.ObjectPool;
public abstract class AStar
{
/**
* Executes a path search on the provided data structures.
*
* @param openList The open list to be used while searching.
* @param closedList The closed list to be used while searching.
* @param map The search space the A* algorithm operates on and retreives
* tiles from.
* @param goal The goal object that provides data about goal tile, heuristic
* function, etc.
* @param nodePool The object pool that is to provide nodes to the algorithm.
* @param usedVisitor The visitor that is to be used for the map.
*
* @return A path from start node to goal node. <code>null</code> if no path
* was found.
*/
public static <T extends AStarNodeBase<T>> List<T> findPath(AStarOpenListBase<T> openList, AStarClosedListBase<T> closedList,
AStarMapBase<T> map, AStarGoalBase<T> goal, ObjectPool<T> nodePool, AStarMapVisitorBase<T> usedVisitor)
{
T currentNode;
int currentRevolutions = 0;
while (true)
{
// Get the best choice so far
currentNode = openList.removeCheapestOpenNode();
if (currentNode == null)
break;
// If this returns true, then it's likely that we are not at the
// goal and we have no more nodes to search through.
if (goal.isPathFinished(currentNode))
break;
// Tell the map we want to evaluate the current node's neighbours
map.visitNeighboursOf(currentNode, usedVisitor);
currentRevolutions++;
if (goal.shouldGiveUp(currentRevolutions))
break;
/*
* We're done with the current node, move it to closed list.
*
* IMPORTANT: This is done after checking for giving up on purpose: It
* ensures that the current node is not stored both in the currentNode
* variable and in the closed list at the same time. In the case we give
* up searching, this simplifies the memory cleanup a bit, because it
* doesn't need to check for this "duplicate" reference.
*/
closedList.addNodeToClosedList(currentNode);
}
// Check if we arrived at the goal. If so, construct a path.
List<T> path = null;
if (currentNode != null && goal.distanceToGoal(currentNode.getX(), currentNode.getY(), currentNode.getZ()) == 0)
{
path = traceBackPath(currentNode);
currentNode = null;
}
// Clean up memory
openList.clearOpenList();
closedList.clearClosedList();
return path;
}
private static <T extends AStarNodeBase<T>> List<T> traceBackPath(T goalNode)
{
List<T> path = new LinkedList<T>();
T currentNode = goalNode;
path.add(currentNode);
while (currentNode.origin != null)
{
currentNode = currentNode.origin;
path.add(currentNode);
}
java.util.Collections.reverse(path);
return path;
}
}