public void Test1()
{
Node A = new Node(1);
Assert.AreEqual(true, _07.CheckLinkedListPalindromeUsingStack(A));
Assert.AreEqual(true, _07.CheckLinkedListPalindromeRecursive(A, 1).isPalindrome);
}
public static Node DeleteNthLastElement(Node head, int posFromLast)
{
Node p1 = head;
Node p2 = head;
while (p1.next != null)
{
if (posFromLast <= 0)
{
p2 = p2.next;
}
p1 = p1.next;
posFromLast--;
}
if (posFromLast > 0)
{
return head.next;
}
else
{
p2.next = p2.next.next;
return head;
}
}
public static void DeleteNodeGivenNode(Node node)
{
if (node == null || node.next == null)
{
throw new ElementOutOfBoundsException();
}
node.value = node.next.value;
node.next = node.next.next;
}
public void Test2()
{
Node A = new Node(1);
Node B = new Node(2);
Node C = new Node(1);
A.next = B;
B.next = C;
Assert.AreEqual(true, _07.CheckLinkedListPalindromeUsingStack(A));
Assert.AreEqual(true, _07.CheckLinkedListPalindromeRecursive(A, 3).isPalindrome);
}
public void TestReverse()
{
Node n1 = new Node(9);
n1.next = new Node(9);
n1.next.next = new Node(9);
Node n2 = new Node(9);
n2.next = new Node(9);
n2.next.next = new Node(9);
Node result = _05.AddLinkedListReverse(n1, n2);
}
public void TestForward()
{
Node n1 = new Node(9);
n1.next = new Node(9);
n1.next.next = new Node(9);
Node n2 = new Node(9);
n2.next = new Node(9);
n2.next.next = new Node(9);
n2.next.next.next = new Node(9);
Node result = _05.AddLinkedListForward(n1, n2);
}
public void Test1()
{
Node head = new Node(2);
Node ptr = head;
foreach (int num in new int[] {8, 9, 2, 1, 9, 9, 5, 5, 7, 0}){
ptr.next = new Node(num);
ptr = ptr.next;
}
head.PrintTail();
_01.RemoveDuplicates(head);
head.PrintTail();
}
public void TestRecursive()
{
Node n1 = new Node(9);
n1.next = new Node(9);
n1.next.next = new Node(9);
Node n2 = new Node(9);
n2.next = new Node(9);
n2.next.next = new Node(9);
n2.next.next.next = new Node(9);
Node result = _05.RecursiveReverse(n1, n2, 0);
}
// Stack can be used to reverse a linked list
public static Node AddLinkedListForward(Node l1, Node l2)
{
Stack<int> stack1 = new Stack<int>();
Stack<int> stack2 = new Stack<int>();
while (l1 != null)
{
stack1.Push(l1.value);
l1 = l1.next;
}
while (l2 != null)
{
stack2.Push(l2.value);
l2 = l2.next;
}
// after reversing the list with a stack it's essentially the same concept as before
int carry = 0;
int sum;
Node head = null;
while (stack1.Count != 0 || stack2.Count != 0)
{
if (stack1.Count > 0 && stack2.Count > 0)
{
sum = stack1.Pop() + stack2.Pop() + carry;
}
else if (stack1.Count > 0)
{
sum = stack1.Pop() + carry;
}
else
{
sum = stack2.Pop() + carry;
}
Node newNode = new Node(sum % 10);
carry = sum / 10;
newNode.next = head;
head = newNode;
}
if (carry == 1)
{
Node newNode = new Node(1);
newNode.next = head;
head = newNode;
}
return head;
}
public void Test2()
{
Node head = new Node(1);
Node ptr = head;
foreach (int num in new int[] { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 })
{
ptr.next = new Node(num);
ptr = ptr.next;
}
head.PrintTail();
_01.RemoveDuplicates(head);
head.PrintTail();
}
public void Test()
{
Random rand = new Random();
Node head = new Node(rand.Next(0, 10));
Node ptr = head;
for (int i = 0; i < 10; i++)
{
ptr.next = new Node(rand.Next(0, 10));
ptr = ptr.next;
}
head.PrintTail();
_01.RemoveDuplicates(head);
head.PrintTail();
}
public static Node PartitionList(Node node, int x)
{
Node leftHead = null;
Node left = null;
Node rightHead = null;
Node right = null;
while (node != null)
{
if (node.value <= x)
{
if (leftHead == null)
{
leftHead = node;
left = node;
}
else
{
left.next = node;
left = left.next;
}
}
else
{
if (rightHead == null)
{
rightHead = node;
right = node;
}
else
{
right.next = node;
right = right.next;
}
}
node = node.next;
}
if (left != null)
{
left.next = rightHead;
return leftHead;
}
return rightHead;
}
public void Test()
{
Node A = new Node(1);
Node B = new Node(2);
Node C = new Node(3);
Node D = new Node(4);
Node E = new Node(5);
Node F = new Node(6);
A.next = B;
B.next = C;
C.next = D;
D.next = E;
E.next = F;
F.next = D;
Node result = _06.BeginningOfLoop(A);
}
public void Test()
{
Node A = new Node(1);
Node B = new Node(2);
Node C = new Node(3);
Node D = new Node(3);
Node E = new Node(2);
Node F = new Node(1);
A.next = B;
B.next = C;
C.next = D;
D.next = E;
E.next = F;
Assert.AreEqual(true, _07.CheckLinkedListPalindromeUsingStack(A));
Assert.AreEqual(true, _07.CheckLinkedListPalindromeRecursive(A, 6).isPalindrome);
}
/*
* ! - Exclamation point denotes collision point
* [A!] -> B -> C -> [A] | collision point 0 away from beginning of loop A
* BEFORE LOOP (empty)
* A -> [B] -> C -> D! -> [B] | collision point 1 away from beginning of loop B
* - BEFORE LOOP size = 1
* A -> B -> [C] -> D! -> E -> [C] | collision point 2 away from beginning of loop C
* ------ BEFORE LOOP size = 2
* A -> B -> C -> [D!] -> E -> F -> [D] | collision point 0 away from beginning of loop D
* ----------- BEFORE LOOP size = 3
* A -> B -> C -> D -> [E] -> F -> G! -> [E] | collision point 1 away from beginning of loop E
* ---------------- BEFORE LOOP size = 4
*
* We can then essentially deduce BEFORE_LOOP % LOOP_SIZE = how far the collision away is from the beginning.
* Since we know there must be a loop, BEFORE LOOP must be a multiple of how far away the collision point is from the beginning of the loop (or the collision point would be in a different spot).
* Then we can simply run a pointer from BEFORE LOOP and then continue a pointer from collision point, and the place they collide is the beginning of the loop.
*
* More formally: when the slower pointer takes k steps, the faster pointer will have taken 2k steps. Therefore, the collision would have happened at 2k - k (or k steps).
* When the slower pointer is 0 steps into the loop, the faster pointer will be k % LOOP_SIZE (K from now on) steps into the loop.
* The slower pointer is thus LOOP_SIZE - K distance from the faster pointer.
* Since both pointers are now in a circle, the faster pointer will approach the slower pointer at a rate of 1 node per step.
* Since K is just k % LOOP_SIZE, another pointer sent from the beginning of the list will collide with a pointer resumed from the start of the list, as both are K away from the beginning of the list.
*
*/
public static Node BeginningOfLoop(Node head)
{
Node p1 = head; // step by 1
Node p2 = head; // step by 2
do
{
p1 = p1.next;
p2 = p2.next.next;
}
while (p1 != p2); // This is where they collide
p2 = head; // Move to start of list, now move by 1
while (p1 != p2)
{
p1 = p1.next;
p2 = p2.next;
}
return p1;
}
public static void RemoveDuplicates(Node head)
{
Node ptr = head.next;
while (ptr != null)
{
Node search = head;
while (search != ptr)
{
// found something, remove value from list
if (search.value == ptr.value)
{
while (search.next != ptr)
{
search = search.next;
}
search.next = ptr.next;
break;
}
search = search.next;
}
ptr = ptr.next;
}
}
/*
* For recursive implementation, first we should consider the base cases:
* 0: obvious
* 1: ( A ( B ) A ) - B does not need to be compared, so A goes with B.next
* 2: ( A ( B1 B2 ) A ) - Though this doesn't seem like a base case (why not use 0)? It is.
* The reason is that if we use 0, instead of comparing B1 B2 we will compare:
* n = A, length = 4
* n = B1, length = 2
* n = B2, length = 0 -> return value is B2.next which is A
* -> n = B1 will end up getting compared to return value B2.next A
*
* The next key thing is that the input is the first half of the list, and the return value is the second half.
* Now you can compare (due to recursive calls) the 0 with n, 1 with n-1, 2 with n-2, etc...
*
* Since we use the return value to get the second half of the list, we need to wrap the return node in a class
* with a boolean result so that we can give an answer at the end.
*/
public static CheckLinkedListPalindromeRecursiveHelper CheckLinkedListPalindromeRecursive(Node n, int length)
{
if (length == 0 || n == null)
{
return new CheckLinkedListPalindromeRecursiveHelper(null, true);
}
if (length == 1)
{
return new CheckLinkedListPalindromeRecursiveHelper(n.next, true);
}
if (length == 2)
{
return new CheckLinkedListPalindromeRecursiveHelper(n.next.next, n.value == n.next.value);
}
CheckLinkedListPalindromeRecursiveHelper res = CheckLinkedListPalindromeRecursive(n.next, length - 2);
if (!res.isPalindrome)
{
return res;
}
else if (n.value != res.node.value)
{
res.isPalindrome = false;
return res;
}
res.node = res.node.next;
return res;
}
public static bool CheckLinkedListPalindromeUsingStack(Node head)
{
Stack<int> stack = new Stack<int>();
Node ptr = head;
while (ptr != null)
{
stack.Push(ptr.value);
ptr = ptr.next;
}
ptr = head;
int numToCompare = stack.Count / 2;
for (int i = 0; i < numToCompare; i++)
{
if (stack.Pop() != ptr.value)
{
return false;
}
ptr = ptr.next;
}
return true;
}
public static Node RecursiveReverse(Node l1, Node l2, int carry)
{
int sum = 0;
if (l1 == null && l2 == null)
{
sum += carry;
if (sum == 0)
{
return null;
}
}
else if (l1 == null)
{
sum = l2.value + carry;
}
else if (l2 == null)
{
sum = l1.value + carry;
}
else
{
sum = l1.value + l2.value + carry;
}
Node rest = RecursiveReverse(l1 == null ? null : l1.next, l2 == null ? null : l2.next, sum / 10);
Node newNode = new Node(sum % 10);
newNode.next = rest;
return newNode;
}
public static Node AddLinkedListReverse(Node l1, Node l2)
{
Node headNode = new Node(0);
Node prevNode = headNode;
int carry = 0;
while (l1 != null || l2 != null)
{
Node newNode = new Node();
// 3 cases
if (l1 == null) // l1 is null, add l2 with any possible carry and go to next node
{
newNode.value = l2.value + carry;
l2 = l2.next;
}
else if (l2 == null) // l2 is null, add l1 with any possible carry and go to next node
{
newNode.value = l1.value + carry;
l1 = l1.next;
}
else // add both numbers and go to next node
{
newNode.value = l1.value + l2.value + carry;
l1 = l1.next;
l2 = l2.next;
}
// if the number has carry can be calculated by dividing the value by 10 since division is rounding towards 0
carry = newNode.value / 10;
// value can be calculated from the modulus
newNode.value = newNode.value % 10;
// set the next node
prevNode.next = newNode;
prevNode = prevNode.next;
}
// perform the last carry
if (carry == 1)
{
Node newNode = new Node();
newNode.value = carry;
prevNode.next = newNode;
}
return headNode.next;
}
public CheckLinkedListPalindromeRecursiveHelper(Node node, bool isPalindrome)
{
this.node = node;
this.isPalindrome = isPalindrome;
}