private List <Point> reconstructPath(AStarCell cell)
{
List <Point> path = new List <Point>();
while (!(cell.getPreviousCell() == null))
{
path.Insert(0, cell.getPoint());
cell = cell.getPreviousCell();
}
path.Insert(0, cell.getPoint());
return(path);
}
public List <Point> calcShortestPath(int startX, int startY, int goalX, int goalY)
{
AStarCell startCell = map.getCell(startX, startY);
AStarCell goalCell = map.getCell(goalX, goalY);
if (startCell == null || startCell.isObstacle())
{
return(null);
}
//Check if the goal cell is also an obstacle (if it is, it is impossible to find a path there)
if (goalCell == null || goalCell.isObstacle())
{
return(null);
}
startCell.reset();
startCell.setDistanceFromStart(0);
closedList.Clear();
openList.Clear();
openList.Add(startCell);
//while we haven't reached the goal yet
while (openList.Count() != 0)
{
//get the first Cell from non-searched Cell list, sorted by lowest distance from our goal as guessed by our heuristic
AStarCell current = openList[0];
// check if our current Cell location is the goal Cell. If it is, we are done.
if (current.getX() == goalX && current.getY() == goalY)
{
return(reconstructPath(current));
}
//move current Cell to the closed (already searched) list
openList.Remove(current);
closedList.Add(current);
//go through all the current Cells neighbors and calculate if one should be our next step
foreach (AStarCell neighbor in current.getNeighborList())
{
bool neighborIsBetter;
//if we have already searched this Cell, don't bother and continue to the next one
if (closedList.Contains(neighbor))
{
continue;
}
//also just continue if the neighbor is an obstacle
if (!neighbor.isObstacle())
{
// calculate how long the path is if we choose this neighbor as the next step in the path
float neighborDistanceFromStart = (current.getDistanceFromStart() + map.getDistanceBetween(current, neighbor));
//add neighbor to the open list if it is not there
if (!openList.Contains(neighbor))
{
neighbor.reset();
openList.Add(neighbor);
neighborIsBetter = true;
//if neighbor is closer to start it could also be better
}
else if (neighborDistanceFromStart < current.getDistanceFromStart())
{
neighborIsBetter = true;
}
else
{
neighborIsBetter = false;
}
// set neighbors parameters if it is better
if (neighborIsBetter)
{
neighbor.setPreviousCell(current);
neighbor.setDistanceFromStart(neighborDistanceFromStart);
neighbor.setHeuristicDistanceFromGoal(heuristic.getEstimatedDistanceToGoal(neighbor.getPoint(), goalCell.getPoint()));
// csharp List.Sort use QuickSort, which is unstable,
// but in java implement ArrayList.sort use MergeSort, which is stable,
// so here use MergeSort to generate the same result as in java implement
MergeSortClass.MergeSort(openList);
}
}
}
}
return(null);
}