public static Node <T> FindOverlapWithHash(EPI.DataStructures.LinkedList.LinkedList <T> aList, EPI.DataStructures.LinkedList.LinkedList <T> bList)
{
HashSet <Node <T> > aNodes = new HashSet <Node <T> >();
Node <T> a = aList.Head;
Node <T> b = bList.Head;
if (a == null || b == null)
{
return(null);
}
while (a != null)
{
aNodes.Add(a);
a = a.Next;
}
while (b != null)
{
if (aNodes.Contains(b))
{
return(b);
}
b = b.Next;
}
return(null);
}
public void NoCycleLengthOne()
{
EPI.DataStructures.LinkedList.LinkedList <Object> list = new EPI.DataStructures.LinkedList.LinkedList <Object>();
Node <Object> a = new Node <object>();
list.Head = a;
a.Next = null;
Assert.Null(C07Q03 <Object> .FindCycleWithDict(list));
Assert.Null(C07Q03 <Object> .FindCycle(list));
Assert.Null(C07Q03 <Object> .FindCycleOptimized(list));
}
public void CycleStartsAtHeadLengthOne()
{
EPI.DataStructures.LinkedList.LinkedList <Object> list = new EPI.DataStructures.LinkedList.LinkedList <Object>();
Node <Object> a = new Node <object>();
list.Head = a;
a.Next = a;
Assert.Equal(a, C07Q03 <Object> .FindCycleWithDict(list));
Assert.Equal(a, C07Q03 <Object> .FindCycle(list));
Assert.Equal(a, C07Q03 <Object> .FindCycleOptimized(list));
}
public void HasCycle01()
{
EPI.DataStructures.LinkedList.LinkedList <Object> list = new EPI.DataStructures.LinkedList.LinkedList <Object>();
Node <Object> a = new Node <object>();
Node <Object> b = new Node <object>();
Node <Object> c = new Node <object>();
list.Head = a;
a.Next = b;
b.Next = c;
c.Next = b;
Assert.Equal(b, C07Q03 <Object> .FindCycleWithDict(list));
Assert.Equal(b, C07Q03 <Object> .FindCycle(list));
Assert.Equal(b, C07Q03 <Object> .FindCycleOptimized(list));
}
public static Node <T> FindCycle(EPI.DataStructures.LinkedList.LinkedList <T> list)
{
if (list.Head == null || list.Head.Next == null)
{
return(null);
}
Node <T> slow = list.Head;
Node <T> fast = list.Head.Next;
while (fast != null && fast != slow)
{
fast = fast.Next?.Next;
slow = slow.Next;
}
if (fast == null)
{
return(null);
}
// fast is currently in a cycle
int cycleLength = 1;
Node <T> seen = fast;
fast = fast.Next;
while (seen != fast)
{
cycleLength++;
fast = fast.Next;
}
Node <T> cycleStart = list.Head;
while (cycleStart != fast)
{
for (int i = 0; i < cycleLength; i++)
{
fast = fast.Next;
if (fast == cycleStart)
{
return(cycleStart);
}
}
cycleStart = cycleStart.Next;
}
return(cycleStart);
}
public static Node <T> FindCycleWithDict(EPI.DataStructures.LinkedList.LinkedList <T> list)
{
Node <T> current = list.Head;
HashSet <Node <T> > visited = new HashSet <Node <T> >();
while (current != null)
{
if (visited.Contains(current))
{
return(current);
}
visited.Add(current);
current = current.Next;
}
return(null);
}
public void SameHead()
{
EPI.DataStructures.LinkedList.LinkedList <Object> listA = new EPI.DataStructures.LinkedList.LinkedList <Object>();
EPI.DataStructures.LinkedList.LinkedList <Object> listB = new EPI.DataStructures.LinkedList.LinkedList <Object>();
Node <Object> aa = new Node <object>();
Node <Object> ab = new Node <object>();
Node <Object> ac = new Node <object>();
listA.Head = aa;
listB.Head = aa;
aa.Next = ab;
ab.Next = ac;
ac.Next = null;
Assert.Equal(aa, C07Q04 <Object> .FindOverlapWithHash(listA, listB));
Assert.Equal(aa, C07Q04 <Object> .FindOverlapBruteForce(listA, listB));
Assert.Equal(aa, C07Q04 <Object> .FindOverlap(listA, listB));
}
public static Node <T> FindOverlap(EPI.DataStructures.LinkedList.LinkedList <T> aList, EPI.DataStructures.LinkedList.LinkedList <T> bList)
{
Node <T> a = aList.Head;
Node <T> b = bList.Head;
Node <T> longer, shorter;
int aLen = 0;
int bLen = 0;
while (a != null)
{
aLen++;
a = a.Next;
}
while (b != null)
{
bLen++;
b = b.Next;
}
if (aLen > bLen)
{
longer = aList.Head;
shorter = bList.Head;
}
else
{
longer = bList.Head;
shorter = aList.Head;
}
for (int i = 0; i < Math.Abs(aLen - bLen); i++)
{
longer = longer.Next;
}
while (longer != null && longer != shorter)
{
longer = longer.Next;
shorter = shorter.Next;
}
return(longer);
}
public static Node <T> FindOverlapBruteForce(EPI.DataStructures.LinkedList.LinkedList <T> aList, EPI.DataStructures.LinkedList.LinkedList <T> bList)
{
Node <T> a = aList.Head;
Node <T> b;
while (a != null)
{
b = bList.Head;
while (b != null)
{
if (a == b)
{
return(b);
}
b = b.Next;
}
a = a.Next;
}
return(null);
}
public void CycleAtTailLengthOne()
{
EPI.DataStructures.LinkedList.LinkedList <Object> list = new EPI.DataStructures.LinkedList.LinkedList <Object>();
Node <Object> a = new Node <object>();
Node <Object> b = new Node <object>();
Node <Object> c = new Node <object>();
Node <Object> d = new Node <object>();
Node <Object> e = new Node <object>();
Node <Object> f = new Node <object>();
list.Head = a;
a.Next = b;
b.Next = c;
c.Next = d;
d.Next = e;
e.Next = f;
f.Next = f;
Assert.Equal(f, C07Q03 <Object> .FindCycleWithDict(list));
Assert.Equal(f, C07Q03 <Object> .FindCycle(list));
Assert.Equal(f, C07Q03 <Object> .FindCycleOptimized(list));
}
public void NoOverlap()
{
EPI.DataStructures.LinkedList.LinkedList <Object> listA = new EPI.DataStructures.LinkedList.LinkedList <Object>();
EPI.DataStructures.LinkedList.LinkedList <Object> listB = new EPI.DataStructures.LinkedList.LinkedList <Object>();
Node <Object> aa = new Node <object>();
Node <Object> ab = new Node <object>();
Node <Object> ba = new Node <object>();
Node <Object> bb = new Node <object>();
Node <Object> bc = new Node <object>();
Node <Object> bd = new Node <object>();
listA.Head = aa;
aa.Next = ab;
ab.Next = null;
listB.Head = ba;
ba.Next = bb;
bb.Next = bc;
bc.Next = bd;
bd.Next = null;
Assert.Null(C07Q04 <Object> .FindOverlapWithHash(listA, listB));
Assert.Null(C07Q04 <Object> .FindOverlapBruteForce(listA, listB));
Assert.Null(C07Q04 <Object> .FindOverlap(listA, listB));
}
