private static Result FindSplit(ArrayList dataArray, Interval bounds, int intervals, float optimum, ResultCache cache)
{
#if PERFCOUNTERS
recursionCount++;
#endif
#if SCOREGRAPH
bool topLevel = (bounds.Left == 0) && (bounds.Right == dataArray.Count);
#endif
// check if there is enough split points
Debug.Assert(bounds.Right - bounds.Left >= intervals);
// test the end of recursion (no splitting)
if (intervals == 1)
{
Result result = new Result();
result.Intervals.Add(bounds);
int count = 0;
for (int i = bounds.Left; i < bounds.Right; i++)
count += ((Data) dataArray[i]).Count;
result.Cost = ResultPenalty(count, optimum);
return result;
}
// test the end of recursion (exact splitting, no choice)
if (intervals == bounds.Right - bounds.Left)
{
Result result = new Result();
result.Cost = 0.0f;
for (int i = bounds.Left; i < bounds.Right; i++)
{
result.Intervals.Add(new Interval(i, i + 1));
result.Cost += ResultPenalty(((Data) dataArray[i]).Count, optimum);
}
return result;
}
// cache lookup
{
Result result = cache.GetResult(intervals, bounds);
if (result != null)
return result;
}
// count objects that must be in the left part
int leftIntervals = intervals / 2;
int leftSum = 0;
for (int i = 0; i < leftIntervals; i++)
leftSum += ((Data) dataArray[bounds.Left + i]).Count;
// add some more intervals until optimal point is reached
int bestSplit;
int leftOptimalSum = (int) Math.Round(optimum * leftIntervals);
for (bestSplit = bounds.Left + leftIntervals; bestSplit < bounds.Right - (intervals - leftIntervals); bestSplit++)
{
if (leftSum + ((Data) dataArray[bestSplit]).Count > leftOptimalSum)
break;
leftSum += ((Data) dataArray[bestSplit]).Count;
}
// start testing these split points (spreading to left and right)
int leftSplit = bestSplit;
int rightSplit = bestSplit + 1;
bool leftStop = false; // there's always at least one solution
bool rightStop = (rightSplit > bounds.Right - (intervals - leftIntervals)); // go right only if there is another possible split point
// spread to both sides and search for better solutions
Result bestResult = new Result(), leftTmpResult, rightTmpResult;
bestResult.Cost = initPenalty;
float leftLastScore = initPenalty, rightLastScore = initPenalty;
int leftGrowCount = 0, rightGrowCount = 0;
while (!leftStop || !rightStop)
{
if (!leftStop)
{
// find solution for left and right part
leftTmpResult = FindSplit(dataArray, new Interval(bounds.Left, leftSplit), leftIntervals, optimum, cache);
rightTmpResult = FindSplit(dataArray, new Interval(leftSplit, bounds.Right), intervals - leftIntervals, optimum, cache);
// sum the costs of partial results
float sum = leftTmpResult.Cost + rightTmpResult.Cost;
#if SCOREGRAPH
if (topLevel)
{
// top level in the recursion
Trace.WriteLine(String.Format("{0};{1}", leftSplit, sum));
}
#endif
// first solution is propagated to the right side
if (rightLastScore == initPenalty)
{
// save to right last value
rightLastScore = sum;
}
// compare this result to what we have so far
if (sum < bestResult.Cost)
{
// merge two partial solution to one
bestResult.Merge(leftTmpResult, rightTmpResult);
// absolute stop criterium (perfect result)
if (sum == 0.0f)
break;
}
#if SCOREGRAPH
if (!topLevel)
{
#endif
// check stop criterium (result penalty is too big)
if (sum > stopLimit * bestResult.Cost)
{
// stop spreading to the left
leftStop = true;
}
// check stop criterium (result penalty is constantly growing, so there is
// probably no hope of getting better result than we have...)
if (sum < leftLastScore)
{
// not growing, reset the counter
leftGrowCount = 0;
}
else
{
// growing, increase
leftGrowCount++;
if (leftGrowCount == growLimit)
leftStop = true;
}
leftLastScore = sum;
#if SCOREGRAPH
}
#endif
// check if there is possibility to spread further to the left
if (leftSplit <= bounds.Left + leftIntervals)
{
// stop testing spreading to the left
leftStop = true;
}
else
{
// shift the left split to the next position
leftSplit--;
}
}
if (!rightStop)
{
// find solution for left and right part
leftTmpResult = FindSplit(dataArray, new Interval(bounds.Left, rightSplit), leftIntervals, optimum, cache);
rightTmpResult = FindSplit(dataArray, new Interval(rightSplit, bounds.Right), intervals - leftIntervals, optimum, cache);
// sum the costs of partial results
float sum = leftTmpResult.Cost + rightTmpResult.Cost;
#if SCOREGRAPH
if (topLevel)
{
// top level in the recursion
Trace.WriteLine(String.Format("{0};{1}", rightSplit, sum));
}
#endif
// compare this result to what we have so far
if (sum < bestResult.Cost)
{
// merge two partial solution to one
bestResult.Merge(leftTmpResult, rightTmpResult);
}
#if SCOREGRAPH
if (!topLevel)
{
#endif
// check stop criterium (result penalty is too big)
if (sum > stopLimit * bestResult.Cost)
{
// stop testing spreading to the right
rightStop = true;
}
// check stop criterium (result penalty is constantly growing, so there is
// probably no hope of getting better result than we have...)
if (sum < rightLastScore)
{
// not growing, reset the counter
rightGrowCount = 0;
}
else
{
// growing, increase
rightGrowCount++;
if (rightGrowCount == growLimit)
rightStop = true;
}
rightLastScore = sum;
#if SCOREGRAPH
}
#endif
// check if there is possibility to spread further to the right
if (rightSplit >= bounds.Right - (intervals - leftIntervals))
{
// stop testing spreading to the right
rightStop = true;
}
else
{
// shift the right split to the next position
rightSplit++;
}
}
}
// check the solution
Debug.Assert(bestResult.Cost < initPenalty);
// add the best result to cache
cache.SetResult(intervals, bounds, bestResult);
// ...and return it
return bestResult;
}
