public ListNode SwapPairs(ListNode head)
{
if (head == null || head.next == null) return head;
ListNode newHead = head.next;
var left = head;
var right = head.next;
ListNode current = null;
while (left != null && right != null)
{
var origLeft = left;
var nextPair = right.next;
left = right;
left.next = origLeft;
origLeft.next = nextPair;
if (current != null)
{
current.next = right;
}
current = origLeft;
if (nextPair == null)
{
break;
}
left = nextPair;
right = nextPair.next;
}
return newHead;
}
public void ConfirmGetValueOfLargeNumber()
{
var list2_1 = new ListNode(1);
var list2_2 = new ListNode(9);
var list2_3 = new ListNode(9);
var list2_4 = new ListNode(9);
var list2_5 = new ListNode(9);
var list2_6 = new ListNode(9);
var list2_7 = new ListNode(9);
var list2_8 = new ListNode(9);
var list2_9 = new ListNode(9);
var list2_10 = new ListNode(9);
list2_1.next = list2_2;
list2_2.next = list2_3;
list2_3.next = list2_4;
list2_4.next = list2_5;
list2_5.next = list2_6;
list2_6.next = list2_7;
list2_7.next = list2_8;
list2_8.next = list2_9;
list2_9.next = list2_10;
var value = GetValueOfList(list2_1);
Assert.That(value, Is.EqualTo(9999999991));
}
public void ConfirmGetValueOfZeroList()
{
var list = new ListNode(0);
var value = GetValueOfList(list);
value.Should().Be(0);
}
public ListNode AddTwoNumbers(ListNode l1, ListNode l2)
{
var firstValue = GetValueOfList(l1);
var secondValue = GetValueOfList(l2);
var sum = firstValue + secondValue;
return TurnValueIntoList(sum);
}
public ListNode RemoveNthFromEnd(ListNode head, int n)
{
if (head == null) return null;
if (head.next == null) return null;
var queue = new Queue<ListNode>();
var current = head;
do
{
queue.Enqueue(current);
current = current.next;
while (queue.Count > n)
{
queue.Dequeue();
}
} while (current != null && current.next != null);
var removingFirst = n > queue.Count;
ListNode nodeToLinkForward;
if (removingFirst)
{
queue.Dequeue();
if (queue.Count > 0)
{
nodeToLinkForward = queue.Dequeue();
}
else
{
nodeToLinkForward = current;
}
}
else
{
nodeToLinkForward = queue.Dequeue();
if (queue.Count > 0)
{
queue.Dequeue();
if (queue.Count > 0)
{
nodeToLinkForward.next = queue.Dequeue();
}
else
{
nodeToLinkForward.next = current;
}
}
else
{
nodeToLinkForward.next = null;
}
}
return removingFirst ? nodeToLinkForward : head;
}
public void RemoveLastNodeFromTwo()
{
var node1 = new ListNode(1);
var node2 = new ListNode(2);
node1.next = node2;
var result = RemoveNthFromEnd(node1, 1);
Assert.That(result.val, Is.EqualTo(1));
Assert.That(result.next, Is.Null);
}
public void MergeSingleItemListsWithL2HavingSmallerValue()
{
var list1Node1 = new ListNode(2);
var list2Node1 = new ListNode(1);
var result = MergeTwoLists(list1Node1, list2Node1);
Assert.That(result.val, Is.EqualTo(1));
Assert.That(result.next.val, Is.EqualTo(2));
Assert.That(result.next.next, Is.Null);
}
public void RemoveFirstNodeFromThree()
{
var node1 = new ListNode(1);
var node2 = new ListNode(2);
var node3 = new ListNode(3);
node1.next = node2;
node2.next = node3;
var result = RemoveNthFromEnd(node1, 3);
Assert.That(result.val, Is.EqualTo(2));
Assert.That(result.next.val, Is.EqualTo(3));
Assert.That(result.next.next, Is.Null);
}
public void MergeShort1ToLong2()
{
var list1Node1 = new ListNode(1);
var list2Node1 = new ListNode(2);
var list2Node2 = new ListNode(3);
var list2Node3 = new ListNode(4);
list2Node1.next = list2Node2;
list2Node2.next = list2Node3;
var result = MergeTwoLists(list1Node1, list2Node1);
Assert.That(result.val, Is.EqualTo(1));
Assert.That(result.next.val, Is.EqualTo(2));
Assert.That(result.next.next.val, Is.EqualTo(3));
Assert.That(result.next.next.next.val, Is.EqualTo(4));
Assert.That(result.next.next.next.next, Is.Null);
}
public ListNode MergeKLists(ListNode[] lists)
{
if (lists == null || lists.Length == 0) return null;
if (lists.Length == 1) return lists[0];
ListNode head = null;
ListNode current = null;
var toManipulate = new List<ListNode>(lists.Where(l => l != null));
while (toManipulate.Count > 0)
{
int lowestValue = int.MaxValue;
int lowestIdx = 0;
for (var idx = 0; idx < toManipulate.Count; ++idx)
{
if (toManipulate[idx].val < lowestValue)
{
lowestValue = toManipulate[idx].val;
lowestIdx = idx;
}
}
if (head == null)
{
head = toManipulate[lowestIdx];
current = head;
}
else
{
current.next = toManipulate[lowestIdx];
current = current.next;
}
var next = toManipulate[lowestIdx].next;
if (next == null)
{
toManipulate.RemoveAt(lowestIdx);
}
else
{
toManipulate[lowestIdx] = next;
}
}
return head;
}
public void RunExample()
{
// [-2,5]
// [-9,-6,-3,-1,1,6]
var list1Node1 = new ListNode(-2);
var list1Node2 = new ListNode(5);
list1Node1.next = list1Node2;
var list2Node1 = new ListNode(-9);
var list2Node2 = new ListNode(-6);
var list2Node3 = new ListNode(-3);
var list2Node4 = new ListNode(-1);
var list2Node5 = new ListNode(1);
var list2Node6 = new ListNode(6);
list2Node1.next = list2Node2;
list2Node2.next = list2Node3;
list2Node3.next = list2Node4;
list2Node4.next = list2Node5;
list2Node5.next = list2Node6;
var result = MergeTwoLists(list1Node1, list2Node1);
Assert.That(result.val, Is.EqualTo(-9));
Assert.That(result.next.val, Is.EqualTo(-6));
Assert.That(result.next.next.val, Is.EqualTo(-3));
Assert.That(result.next.next.next.val, Is.EqualTo(-2));
Assert.That(result.next.next.next.next.val, Is.EqualTo(-1));
Assert.That(result.next.next.next.next.next.val, Is.EqualTo(1));
Assert.That(result.next.next.next.next.next.next.val, Is.EqualTo(5));
Assert.That(result.next.next.next.next.next.next.next.val, Is.EqualTo(6));
}
public ListNode MergeTwoLists(ListNode l1, ListNode l2)
{
if (l1 == null)
{
return l2;
}
if (l2 == null)
{
return l1;
}
var head = l1;
var left = l1;
var right = l2;
if (l1.val > l2.val)
{
head = l2;
left = l2;
right = l1;
}
while (left != null && right != null)
{
if (left.next != null)
{
while (left.next != null && left.next.val <= right.val)
{
left = left.next;
}
}
else
{
left.next = right;
break;
}
var leftNext = left.next;
left.next = right;
if (leftNext == null) break;
left = right;
right = leftNext;
}
return head;
}
private static ListNode GenerateList(int[] values)
{
ListNode first = new ListNode(values[0]);
ListNode previous = first;
for(var idx = 1; idx < values.Length; ++idx)
{
var next = new ListNode(values[idx]);
previous.next = next;
previous = next;
}
return first;
}
public ListNode ReverseKGroup(ListNode head, int k)
{
if (k < 2) return head;
ListNode newHead = null;
ListNode lastGroupEnd = null;
ListNode current = head;
ListNode startGroup = null;
var stack = new Stack<ListNode>();
do
{
if (stack.Count == k)
{
var groupNode = stack.Pop();
if (lastGroupEnd == null)
{
newHead = groupNode;
}
else
{
lastGroupEnd.next = groupNode;
}
while (stack.Count > 0)
{
var temp = stack.Pop();
groupNode.next = temp;
groupNode = temp;
}
lastGroupEnd = groupNode;
startGroup = current;
}
stack.Push(current);
if (current != null)
{
current = current.next;
}
} while (current != null);
if (stack.Count == k)
{
var groupNode = stack.Pop();
if (newHead == null) newHead = groupNode;
var startFinalGroup = groupNode;
while (stack.Count > 0)
{
var temp = stack.Pop();
groupNode.next = temp;
groupNode = temp;
}
groupNode.next = null;
if (lastGroupEnd != null)
{
lastGroupEnd.next = startFinalGroup;
}
return newHead;
}
else
{
if (lastGroupEnd != null)
{
lastGroupEnd.next = startGroup;
}
}
return newHead ?? head;
}
public void SingleNodeGroupOf2()
{
var list = new ListNode(1);
var result = ReverseKGroup(list, 2);
Assert.That(result.val, Is.EqualTo(1));
Assert.That(result.next, Is.Null);
}
public void RunZeroValueTest()
{
var list1_1 = new ListNode(0);
var list2_1 = new ListNode(0);
var result = AddTwoNumbers(list1_1, list2_1);
result.val.Should().Be(0);
}
public ListNode TurnValueIntoList(long value)
{
int lastDigit = GetLastDigit(value);
var listNode = new ListNode(lastDigit);
var currentNode = listNode;
while (value >= 0)
{
value /= 10;
lastDigit = GetLastDigit(value);
if (value == 0) break;
var nextNode = new ListNode(lastDigit);
currentNode.next = nextNode;
currentNode = nextNode;
}
return listNode;
}
public void RunTenBillionTest()
{
var list1_1 = new ListNode(9);
var list2_1 = new ListNode(1);
var list2_2 = new ListNode(9);
var list2_3 = new ListNode(9);
var list2_4 = new ListNode(9);
var list2_5 = new ListNode(9);
var list2_6 = new ListNode(9);
var list2_7 = new ListNode(9);
var list2_8 = new ListNode(9);
var list2_9 = new ListNode(9);
var list2_10 = new ListNode(9);
list2_1.next = list2_2;
list2_2.next = list2_3;
list2_3.next = list2_4;
list2_4.next = list2_5;
list2_5.next = list2_6;
list2_6.next = list2_7;
list2_7.next = list2_8;
list2_8.next = list2_9;
list2_9.next = list2_10;
var result = AddTwoNumbers(list1_1, list2_1);
var value = GetValueOfList(result);
Assert.That(value, Is.EqualTo(10000000000));
result.val.Should().Be(0);
result.next.val.Should().Be(0);
result.next.next.val.Should().Be(0);
result.next.next.next.val.Should().Be(0);
result.next.next.next.next.val.Should().Be(0);
result.next.next.next.next.next.val.Should().Be(0);
result.next.next.next.next.next.next.val.Should().Be(0);
result.next.next.next.next.next.next.next.val.Should().Be(0);
result.next.next.next.next.next.next.next.next.val.Should().Be(0);
result.next.next.next.next.next.next.next.next.next.val.Should().Be(0);
result.next.next.next.next.next.next.next.next.next.next.val.Should().Be(1);
}
public void RunTest()
{
var list1_1 = new ListNode(2);
var list1_2 = new ListNode(4);
var list1_3 = new ListNode(3);
list1_1.next = list1_2;
list1_2.next = list1_3;
var list2_1 = new ListNode(5);
var list2_2 = new ListNode(6);
var list2_3 = new ListNode(4);
list2_1.next = list2_2;
list2_2.next = list2_3;
var result = AddTwoNumbers(list1_1, list2_1);
result.val.Should().Be(7);
result.next.val.Should().Be(0);
result.next.next.val.Should().Be(8);
}
public long GetValueOfList(ListNode listNode)
{
long value = 0;
long multiplier = 1;
do
{
value += (listNode.val*multiplier);
listNode = listNode.next;
multiplier *= 10;
} while (listNode != null && listNode.next != null);
if (listNode != null)
value += (listNode.val*multiplier);
return value;
}
public void ConfirmValueExtractor()
{
var list1_1 = new ListNode(2);
var list1_2 = new ListNode(4);
var list1_3 = new ListNode(3);
list1_1.next = list1_2;
list1_2.next = list1_3;
var value = GetValueOfList(list1_1);
value.Should().Be(342);
var list2_1 = new ListNode(5);
var list2_2 = new ListNode(6);
var list2_3 = new ListNode(4);
list2_1.next = list2_2;
list2_2.next = list2_3;
value = GetValueOfList(list2_1);
value.Should().Be(465);
}
public void RunTest()
{
var list1Node1 = new ListNode(1);
var list1Node2 = new ListNode(2);
list1Node1.next = list1Node2;
var list2Node1 = new ListNode(2);
var list2Node2 = new ListNode(3);
list2Node1.next = list2Node2;
var result = MergeTwoLists(list1Node1, list2Node1);
Assert.That(result.val, Is.EqualTo(1));
Assert.That(result.next.val, Is.EqualTo(2));
Assert.That(result.next.next.val, Is.EqualTo(2));
Assert.That(result.next.next.next.val, Is.EqualTo(3));
Assert.That(result.next.next.next.next, Is.Null);
}
public void RunExample()
{
var node1 = new ListNode(1);
var node2 = new ListNode(2);
var node3 = new ListNode(3);
var node4 = new ListNode(4);
var node5 = new ListNode(5);
node1.next = node2;
node2.next = node3;
node3.next = node4;
node4.next = node5;
var result = RemoveNthFromEnd(node1, 2);
Assert.That(result, Is.Not.Null, "Have head");
Assert.That(result.val, Is.EqualTo(1), "Head 1");
Assert.That(result.next, Is.Not.Null, "Head + 1");
Assert.That(result.next.val, Is.EqualTo(2), "2");
Assert.That(result.next.next.val, Is.EqualTo(3), "3");
Assert.That(result.next.next.next.val, Is.EqualTo(5), "5");
Assert.That(result.next.next.next.next, Is.Null, "End of list");
}
public void SingleNodeList()
{
var node = new ListNode(1);
var result = RemoveNthFromEnd(node, 1);
Assert.That(result, Is.Null);
}