public ListNode RemoveNthFromEnd(ListNode head, int n)
{
if (head == null)
return null;
if (head.next == null && n >= 1)
return null;
ListNode start = new ListNode(0);
ListNode slow = start, fast = start;
start.next = head;
for (int i = 0; i < n; i++)
{
fast = fast.next;
}
//Move fast to the end, maintaining the gap
while (fast.next != null)
{
slow = slow.next;
fast = fast.next;
}
//Skip the desired node
slow.next = slow.next.next;
return start.next;
}
public ListNode SwapPairs1(ListNode head)
{
if (head == null)
return null;
if (head.next == null)
return head;
ListNode oddList = new ListNode(0);
ListNode oddHead = oddList;
ListNode evenList = new ListNode(0);
ListNode evenHead = evenList;
while (head != null)
{
oddList.next = head;
oddList = oddList.next;
evenList.next = head.next;
if (head.next != null)
{
head = head.next.next;
evenList = evenList.next;
}
if (head == null)
oddList.next = null;
}
ListNode result = new ListNode(0);
ListNode pointer = result;
evenHead = evenHead.next;
oddHead = oddHead.next;
while (oddHead != null && evenHead != null)
{
pointer.next = evenHead;
evenHead = evenHead.next;
pointer = pointer.next;
pointer.next = oddHead;
oddHead = oddHead.next;
pointer = pointer.next;
}
while (oddHead != null)
{
pointer.next = oddHead;
oddHead = oddHead.next;
pointer = pointer.next;
}
return result.next;
}
public ListNode RemoveNthFromEnd1(ListNode head, int n)
{
if (head == null)
return null;
if (head.next == null && n >= 1)
return null;
int index = 0;
head = GetRemovedNext(head, n, ref index);
if (index == n)
{
return head.next;
}
return head;
}
private ListNode GetRemovedNext(ListNode listNode, int n, ref int index)
{
if (listNode.next == null)
{
index = 1;
return listNode;
}
listNode.next = GetRemovedNext(listNode.next, n, ref index);
if (index++ == n)
{
listNode.next = listNode.next.next;
}
return listNode;
}
public ListNode SwapPairs(ListNode head)
{
if (head == null)
return null;
if (head.next == null)
return head;
ListNode result = new ListNode(0);
ListNode pointer = result;
while (head != null && head.next != null)
{
ListNode node = head.next.next;
pointer.next = SwapTwoNodes(head, head.next);
head = node;
pointer = pointer.next.next;
}
return result.next;
}
public void DoIt()
{
ListNode node1 = new ListNode(1);
ListNode node2 = new ListNode(2);
ListNode node3 = new ListNode(3);
ListNode node4 = new ListNode(4);
node1.next = node2;
node2.next = node3;
//node3.next = node4;
ListNode result = SwapPairs(node1);
while (result != null)
{
Console.WriteLine(result.val);
result = result.next;
}
}
public void DoIt()
{
ListNode node1 = new ListNode(1);
ListNode node2 = new ListNode(2);
//ListNode node3 = new ListNode(3);
//ListNode node4 = new ListNode(4);
//ListNode node5 = new ListNode(5);
node1.next = node2;
//node2.next = node3;
//node3.next = node4;
//node4.next = node5;
ListNode result = RemoveNthFromEnd(node1, 1);
while (result != null)
{
Console.WriteLine(result.val);
result = result.next;
}
}
public ListNode MergeTwoLists(ListNode l1, ListNode l2)
{
if (l1 == null) return l2;
if (l2 == null) return l1;
ListNode result = new ListNode(0);
ListNode root = result;
while (l1 != null && l2 != null)
{
if (l1 != null && l2 != null && l1.val <= l2.val)
{
result.next = l1;
l1 = l1.next;
result = result.next;
}
else if (l1 != null && l2 != null && l1.val > l2.val)
{
result.next = l2;
l2 = l2.next;
result = result.next;
}
}
while (l1 != null)
{
result.next = l1;
l1 = l1.next;
result = result.next;
}
while (l2 != null)
{
result.next = l2;
l2 = l2.next;
result = result.next;
}
return root.next;
}
public void DoIt()
{
ListNode node1 = new ListNode(1);
ListNode node2 = new ListNode(2);
ListNode node3 = new ListNode(3);
ListNode node4 = new ListNode(4);
ListNode node5 = new ListNode(5);
ListNode node6 = new ListNode(6);
ListNode node7 = new ListNode(7);
node1.next = node3;
node2.next = node4;
node3.next = node5;
node4.next = node6;
node6.next = node7;
ListNode result = MergeTwoLists(node1, node2);
while (result != null)
{
Console.WriteLine(result.val);
result = result.next;
}
}
private ListNode SwapTwoNodes(ListNode node1, ListNode node2)
{
if (node2 == null)
return null;
ListNode afterNode = node2.next;
node2.next = node1;
node1.next = afterNode;
return node2;
}