static private ReadOnlyIntervalList Normalize(List <Interval> intervals, out bool isBottom)
{
Contract.Requires(intervals != null);
Contract.Ensures(Contract.Result <ReadOnlyIntervalList>() != null);
if (intervals.Count <= 1)
{
isBottom = false;
return(AsReadOnly(intervals));
}
intervals.Sort((a, b) =>
a.Equals(b) ?
0 :
(a.UpperBound <= b.LowerBound ? -1 : 1));
var result = new List <Interval>(intervals.Count);
var bottoms = 0;
var prev = null as Interval;
for (var i = 0; i < intervals.Count; i++)
{
var intv = intervals[i];
// Skip repetitions
if (prev == intv)
{
continue;
}
if (intv.IsBottom)
{
bottoms++;
continue;
}
if (intv.IsTop)
{
isBottom = false;
return(EmptyReadOnlyList);
}
if (prev != null)
{
var refined = true;
while (refined && result.Count > 0)
{
prev = result[result.Count - 1];
if (Interval.AreConsecutiveIntegers(prev, intv)) // The intervals are consecutive, so we join them together
{
result.RemoveAt(result.Count - 1); // remove the last element
intv = prev.Join(intv);
}
else if (prev.LessEqual(intv)) // The last element we added is subsumed by the next one
{
result.RemoveAt(result.Count - 1); // remove the last element
}
else if (intv.LessEqual(prev)) // The last element we added subsumes the next one
{
goto nextIteration;
}
else if (prev.OverlapsWith(intv)) // If they are not included by they overlap, we take the join
{
result.RemoveAt(result.Count - 1); // remove the last element
intv = prev.Join(intv);
}
else
{
refined = false; // Done, we cannot do better
}
}
}
prev = intv;
result.Add(intv);
nextIteration:
;
}
isBottom = bottoms == intervals.Count;
return(AsReadOnly(result));
}