private static void SplitTask(QueenTask baseTask, int numQueens, int levels, Queue <QueenTask> taskQueue)
{
// Base case for recursion.
if (levels == 1)
{
baseTask.id = taskQueue.Count;
taskQueue.Enqueue(baseTask);
return;
}
for (int i = 0; i < numQueens; i++)
{
long queen = 1 << i;
var subTask = baseTask;
subTask.id = 0; // Will be set later.
// No need to set masks[] as it is scratch for the task code.
subTask.solutions = 0;
subTask.step = Step.Place;
subTask.col = (byte)(baseTask.col + 1);
subTask.startCol = (byte)(baseTask.col + 1);
subTask.rook = subTask.rook | queen;
subTask.add |= queen << baseTask.col;
subTask.sub |= queen << (numQueens - 1 - baseTask.col);
subTask.mask = ((1 << numQueens) - 1) & ~(subTask.rook | (subTask.add >> subTask.col) | (subTask.sub >> ((NumQueens - 1) - subTask.col)));
if (Pop(subTask.rook) == subTask.col &&
Pop(subTask.add) == subTask.col &&
Pop(subTask.sub) == subTask.col)
{
SplitTask(subTask, numQueens, levels - 1, taskQueue);
}
}
}
// For an instnace of the N-Queens problem of size n, get a list of QueenTask
// tasks that covers the entire problem. That is, when each task is complete
// the number of solutions found by each task can be summed to determine the
// total number of solutions.
private static Queue <QueenTask> GetQueenTaskPartition(int numQueens, int splitDepth)
{
var wholeProblemTask = new QueenTask();
wholeProblemTask.mask = (1 << numQueens) - 1;
var taskQueue = new Queue <QueenTask>();
SplitTask(wholeProblemTask, numQueens, splitDepth, taskQueue);
return(taskQueue);
}
// For an instnace of the N-Queens problem of size n, get a list of QueenTask
// tasks that covers the entire problem. That is, when each task is complete
// the number of solutions found by each task can be summed to determine the
// total number of solutions.
private static Queue<QueenTask> GetQueenTaskPartition(int numQueens, int splitDepth)
{
var wholeProblemTask = new QueenTask();
wholeProblemTask.mask = (1 << numQueens) - 1;
var taskQueue = new Queue<QueenTask>();
SplitTask(wholeProblemTask, numQueens, splitDepth, taskQueue);
return taskQueue;
}
private static void SplitTask(QueenTask baseTask, int numQueens, int levels, Queue<QueenTask> taskQueue)
{
// Base case for recursion.
if (levels == 1)
{
baseTask.id = taskQueue.Count;
taskQueue.Enqueue(baseTask);
return;
}
for (int i = 0; i < numQueens; i++)
{
long queen = 1 << i;
var subTask = baseTask;
subTask.id = 0; // Will be set later.
// No need to set masks[] as it is scratch for the task code.
subTask.solutions = 0;
subTask.step = Step.Place;
subTask.col = (byte)(baseTask.col + 1);
subTask.startCol = (byte)(baseTask.col + 1);
subTask.rook = subTask.rook | queen;
subTask.add |= queen << baseTask.col;
subTask.sub |= queen << (numQueens - 1 - baseTask.col);
subTask.mask = ((1 << numQueens) - 1) & ~(subTask.rook | (subTask.add >> subTask.col) | (subTask.sub >> ((NumQueens - 1) - subTask.col)));
if (Pop(subTask.rook) == subTask.col &&
Pop(subTask.add) == subTask.col &&
Pop(subTask.sub) == subTask.col)
{
SplitTask(subTask, numQueens, levels - 1, taskQueue);
}
}
}
private static QueenTask[] GetNextAssignment(QueenTask[] inProgress, Queue<QueenTask> todos, IList<QueenTask> done)
{
var nextAssignment = new List<QueenTask>();
foreach (var task in inProgress)
{
if (task.step == Step.Done)
{
done.Add(task);
}
else
{
nextAssignment.Add(task);
}
}
while (nextAssignment.Count < Spread && todos.Any())
nextAssignment.Add(todos.Dequeue());
return nextAssignment.ToArray();
}
