//
// {A1,A2} -> {<A1>,<A2>}
// {A1,A2},{B1,B2} -> {<A1,B1>,<A2,B2>}, {<A1,B2>,<A2,B1>}
// {A1,A2},{B1,B2},{C1,C2} ->
// foreach pair in C({B1,B2},{C1,C2})
// If duplex
// yeild return pair.First + c1, pair.second + c2
// yeild return pair.First + c2, pair.second + c1
// else
// yeild return pair.First + c2, pair.second + c1
// {A1},{B1,B2} -> {<A1,B1>,<A1,B2>}
// {A1} -> {<A1>,<A1>} -> {<A1>}
// {A1},{B1} -> {<A1,B1>,<A1,B1>} -> {<A1,B1>}
//Every item enumerated is unique
static public IEnumerable <UOPair <LinkedList1 <T> > > PhaseEnumeration(LinkedList1 <UOPair <T> > uOPairList)
{
//Use of a singlely-linked list makes this very efficient.
if (null == uOPairList)
{
yield return(UOPair <LinkedList1 <T> > .GetInstance(null, null));
yield break;
}
UOPair <T> firstPair = uOPairList.First();
foreach (UOPair <LinkedList1 <T> > resultsFromRest in PhaseEnumeration(uOPairList.RestOrNull))
{
if (resultsFromRest.ElementsAreSame)
{
if (firstPair.ElementsAreSame)
{
LinkedList1 <T> a0b0 = LinkedList1 <T> .GetInstance(firstPair.First, resultsFromRest.First);
yield return(UOPair <LinkedList1 <T> > .GetInstance(a0b0, a0b0));
}
else
{
LinkedList1 <T> a1b0 = LinkedList1 <T> .GetInstance(firstPair.First, resultsFromRest.First);
LinkedList1 <T> a2b0 = LinkedList1 <T> .GetInstance(firstPair.Second, resultsFromRest.First);
yield return(UOPair <LinkedList1 <T> > .GetInstance(a1b0, a2b0));
}
}
else
{
if (firstPair.ElementsAreSame)
{
LinkedList1 <T> a0b1 = LinkedList1 <T> .GetInstance(firstPair.First, resultsFromRest.First);
LinkedList1 <T> a0b2 = LinkedList1 <T> .GetInstance(firstPair.First, resultsFromRest.Second);
yield return(UOPair <LinkedList1 <T> > .GetInstance(a0b1, a0b2));
}
else
{
LinkedList1 <T> a1b1 = LinkedList1 <T> .GetInstance(firstPair.First, resultsFromRest.First);
LinkedList1 <T> a2b2 = LinkedList1 <T> .GetInstance(firstPair.Second, resultsFromRest.Second);
yield return(UOPair <LinkedList1 <T> > .GetInstance(a1b1, a2b2));
LinkedList1 <T> a1b2 = LinkedList1 <T> .GetInstance(firstPair.First, resultsFromRest.Second);
LinkedList1 <T> a2b1 = LinkedList1 <T> .GetInstance(firstPair.Second, resultsFromRest.First);
yield return(UOPair <LinkedList1 <T> > .GetInstance(a1b2, a2b1));
}
}
}
}
