/// <summary>
/// Checks if a given database contains backward-I-extension event.
/// </summary>
private static bool BackwardIExtensionCheck(ProjectedDatabase projectedDatabase)
{
var lastInLastAppearances = new int[projectedDatabase.Count];
var seqBackwardIExtensionItemset = new HashSet <uint>();
for (int i = projectedDatabase.Prefix.Size - 1; i >= 0; i--)
{
var ei = projectedDatabase.Prefix[i];
var ithBackwardIExtensionItemset = default(HashSet <uint>);
var isIthBackwardIExtensionItemsetEmpty = false;
for (int sid = 0; sid < projectedDatabase.Count; sid++)
{
PseudoSequence sequence = projectedDatabase[sid];
// The i-th I-extensions period of a prefix sequence is defined:
// 1) 1 < i <= n: it is the piece of sequence between the end
// of the first instance of prefix e1e2..ei-1
// and the beginning of the first event after the LLi.
// 2) i == 1: it is the piece of sequence located before the first event after LL1.
int lastInLast = sequence.GetLastInLast(ei, lastInLastAppearances[sid]);
lastInLastAppearances[sid] = lastInLast;
// If ith maximum period is empty just continue fill in lastInLastAppearances for the checking (i-1)-th maximum period.
if (isIthBackwardIExtensionItemsetEmpty)
{
continue;
}
int firstInstance = 0;
if (i != 0)
{
firstInstance = sequence.GetFirstInstance(i) + 1;
}
seqBackwardIExtensionItemset.Clear();
for (; firstInstance <= lastInLast; firstInstance++)
{
if (ei.IsSubsetOf(sequence.RawItems[firstInstance]))
{
seqBackwardIExtensionItemset.UnionWith(sequence.RawItems[firstInstance]);
}
}
seqBackwardIExtensionItemset.ExceptWith(ei);
// ScanSkip:
if (ithBackwardIExtensionItemset == null)
{
ithBackwardIExtensionItemset = new HashSet <uint>(seqBackwardIExtensionItemset);
}
else
{
ithBackwardIExtensionItemset.IntersectWith(seqBackwardIExtensionItemset);
}
// If ith maximum period is empty and i==0 there cant exist any backward-I-extension,
// otherwise if i>0, try find backward-I-extension in (i-1)-th maximum period.
if (ithBackwardIExtensionItemset.Count != 0)
{
continue;
}
if (i == 0)
{
return(false);
}
isIthBackwardIExtensionItemsetEmpty = true;
}
// If all ith maximum periods (in every sequence) contains some items we got a backward-I-extension.
if (ithBackwardIExtensionItemset.Count > 0)
{
return(true);
}
}
return(false);
}
/// <summary>
/// Checks if a given database contains backward-S-extension event.
/// </summary>
private static bool BackwardSExtensionCheck(ProjectedDatabase projectedDatabase)
{
var lastInLastAppearances = new int[projectedDatabase.Count];
var seqMaximumPeriod = new HashSet <uint>();
for (int i = projectedDatabase.Prefix.Size - 1; i >= 0; i--)
{
var ei = projectedDatabase.Prefix[i];
var ithMaximumPeriod = default(HashSet <uint>);
var isIthMaximumPeriodEmpty = false;
for (int sid = 0; sid < projectedDatabase.Count; sid++)
{
PseudoSequence sequence = projectedDatabase[sid];
// The i-th maximum period of a prefix sequence is defined:
// 1) 1 < i <= n: it is the piece of sequence between the end
// of the first instance of prefix e1e2...ei-1 and LLi.
// 2) i == 1: it is the piece of sequence located before the first last-in-last appearance (LL1).
int lastInLast = sequence.GetLastInLast(ei, lastInLastAppearances[sid]);
lastInLastAppearances[sid] = lastInLast;
// If i-th maximum period is empty just continue fill in lastInLastAppearances for the checking (i-1)-th maximum period.
if (isIthMaximumPeriodEmpty)
{
continue;
}
int firstInstance = 0;
if (i != 0)
{
firstInstance = sequence.GetFirstInstance(i) + 1;
}
seqMaximumPeriod.Clear();
for (; firstInstance < lastInLast; firstInstance++)
{
seqMaximumPeriod.UnionWith(sequence.RawItems[firstInstance]);
}
// ScanSkip:
if (ithMaximumPeriod == null)
{
ithMaximumPeriod = new HashSet <uint>(seqMaximumPeriod);
}
else
{
ithMaximumPeriod.IntersectWith(seqMaximumPeriod);
}
// If i-th maximum period is empty and i==0 there cant exist any backward-S-extensions,
// otherwise if i>0, try find backward-S-extensions in (i-1)-th maximum period.
if (ithMaximumPeriod.Count != 0)
{
continue;
}
if (i == 0)
{
return(false);
}
isIthMaximumPeriodEmpty = true;
}
// If all i-th maximum periods (in every sequence) contains any items, we got a backward-S-extension.
if (ithMaximumPeriod.Count != 0)
{
return(true);
}
}
return(false);
}