public ListNode RemoveNthFromEnd2(ListNode head, int n)
{
var s = new Stack<ListNode>();
var t = head;
if (t != null)
{
while (t != null)
{
s.Push(t);
t = t.next;
}
for (var i = 1; i <= n; i++)
{
t = s.Pop();
}
if (t == head)
{
return head.next;
}
if (t.next == null)
{
t = s.Pop();
t.next = null;
return head;
}
t.val = t.next.val;
t.next = t.next.next;
return head;
}
return head;
}
public bool IsPalindrome2(ListNode head)
{
if (head == null || head.next == null)
{
return true;
}
var stack = new Stack<ListNode>();
var tmp = head;
var k = 1;
while (tmp != null)
{
stack.Push(tmp);
tmp = tmp.next;
k++;
}
var h= head;
for (var i = 1; i <= k/2; i++)
{
var t = stack.Pop();
if (h.val != t.val)
{
return false;
}
h = h.next;
}
return true;
}
public ListNode RemoveNthFromEnd(ListNode head, int n)
{
var l = new List<ListNode>();
var t = head;
while (t != null)
{
l.Add(t);
t = t.next;
}
t = head;
for (var i = 1; i < l.Count - n; i++)
{
t.next = l[i];
t = t.next;
}
for (var i = l.Count - n + 1; i < l.Count; i++)
{
t.next = l[i];
t = t.next;
}
t.next = null;
return n==l.Count?head.next:head;
}
public ListNode GetIntersectionNode3(ListNode headA, ListNode headB)
{
if (headA == null || headB == null)
{
return null;
}
var a = headA;
var b = headB;
while (a != b)
{
a = a == null ? headB : a.next;
b = b == null ? headA : b.next;
}
return a;
}
public bool IsPalindrome(ListNode head)
{
if (head == null || head.next == null)
{
return true;
}
var h = head;
var t = h.next;
while (t.next != null)
{
h = t;
t = t.next;
}
h.next = null;
return head.val == t.val && IsPalindrome(head.next);
}
public static ListNode DeleteDuplicates3(ListNode head)
{
if (head == null || head.next == null)
{
return head;
}
head.next = DeleteDuplicates3(head.next);
return head.val == head.next.val ? head.next : head;
}
public static ListNode MergeTwoLists2(ListNode l1, ListNode l2)
{
if (l1 == null)
return l2;
if (l2 == null)
return l1;
ListNode h = null;
var x = l1.val <= l2.val;
h = x ? l1 : l2;
h.next = x ? MergeTwoLists2(l1.next, l2) : MergeTwoLists2(l1, l2.next);
return h;
}
public static ListNode ReverseList1(ListNode head)
{
if (head == null)
{
return null;
}
var nodes = new Stack<ListNode>();
var n = head;
while (n.next != null)
{
nodes.Push(n);
n = n.next;
}
head = n;
while(nodes.Count != 0)
{
n.next = nodes.Pop();
n = n.next;
}
n.next = null;
return head;
}
public static ListNode ReverseList2(ListNode head)
{
if (head == null)
{
return null;
}
var x = head;
var y = head.next;
head.next = null;
while (y != null)
{
var tmp = y.next;
y.next = x;
x = y;
y = tmp;
}
return x;
}
public static ListNode RemoveElements(ListNode head, int val)
{
while (head!=null&&head.val == val)
{
head = head.next;
}
if (head == null)
{
return null;
}
var h = head;
var t = head.next;
while (t != null)
{
if(t.val != val)
{
t = t.next;
h = h.next;
continue;
}
h.next = t.next;
t = t.next;
}
return head;
}
public static ListNode RemoveElements2(ListNode head, int val)
{
if (head == null)
{
return null;
}
if (head.val == val)
{
return RemoveElements2(head.next, val);
}
head.next = RemoveElements2(head.next, val);
return head;
}
public static ListNode OddEvenList3(ListNode head)
{
if (head==null)
{
return null;
}
var odd = head;
var even = head.next;
var evenHead = head.next;
while (even != null && even.next != null)
{
odd.next = odd.next.next;
even.next = even.next.next;
odd = odd.next;
even = even.next;
}
odd.next = evenHead;
return head;
}
public static ListNode OddEvenList2(ListNode head)
{
if (head == null)
{
return null;
}
var o = head;
var e = head.next;
var e1 = e;
while (o.next != null && o.next.next != null)
{
o.next = o.next.next;
o = o.next;
if(e.next != null && e.next.next != null)
{
e.next = e.next.next;
e = e.next;
}
}
o.next = e1;
if (e != null)
{
e.next = null;
}
return head;
}
public static ListNode OddEvenList1(ListNode head)
{
if (head == null || head.next == null)
{
return head;
}
var e = head;
var o = head.next;
var o1 = head.next;
while (e.next!=null&&e.next.next!=null&&o.next!=null&&o.next.next!=null)
{
e.next = e.next.next;
o.next = o.next.next;
e = e.next;
o = o.next;
}
if (o.next != null)
{
e.next = o.next;
e = e.next;
o.next = null;
}
e.next = o1;
return head;
}
public static ListNode DeleteDuplicates1(ListNode head)
{
if (head == null)
{
return null;
}
var h = head;
while (h != null)
{
var n = h.next;
while (n != null && n.val == h.val)
{
n = n.next;
}
h.next = n;
h = h.next;
}
return head;
}
public ListNode GetIntersectionNode(ListNode headA, ListNode headB)
{
var nodeA = headA;
var nodeB = headB;
while (nodeA != null)
{
while (nodeB != null)
{
if (nodeB == nodeA)
{
break;
}
nodeB = nodeB.next;
}
if (nodeB == nodeA)
{
break;
}
nodeA = nodeA.next;
}
return nodeA;
}
public static ListNode DeleteDuplicates2(ListNode head)
{
if (head == null)
{
return null;
}
var p = head;
var q = head.next;
while(q!=null)
{
if (p.val!=q.val)
{
p.next = q;
p = p.next;
}
q= q.next;
}
p.next = null;
return head;
}
// The original structure is changed.
public ListNode GetIntersectionNode2(ListNode headA, ListNode headB)
{
var listA = new Stack<ListNode>();
var listB = new Stack<ListNode>();
while (headA != null)
{
listA.Push(headA);
headA = headA.next;
}
ListNode newHeadA = null;
if (listA.Count != 0)
{
newHeadA = listA.Pop();
var h = newHeadA;
while (listA.Count != 0)
{
h.next = listA.Pop();
h = h.next;
}
h.next = null;
}
while (headB != null)
{
listA.Push(headB);
headB = headB.next;
}
ListNode newHeadB = null;
if (listB.Count != 0)
{
newHeadB = listA.Pop();
var h = newHeadB;
while (listB.Count != 0)
{
h.next = listB.Pop();
h = h.next;
}
h.next = null;
}
ListNode intersection = null;
while (newHeadA == newHeadB && newHeadA!=null && newHeadB!=null)
{
intersection = newHeadA;
newHeadA = newHeadA.next;
newHeadB = newHeadB.next;
}
return intersection;
}
public static void DeleteNode(ListNode node)
{
ListNode next = node.next;
node.val = next.val;
node.next = next.next;
}
public static ListNode MergeTwoLists1(ListNode l1, ListNode l2)
{
if (l1 == null)
{
return l2;
}
if (l2 == null)
{
return l1;
}
ListNode h = null;
if (l1.val <= l2.val)
{
h = l1;
l1 = l1.next;
}
else
{
h = l2;
l2 = l2.next;
}
ListNode m = h;
while (l1 != null && l2 != null)
{
if (l1.val <= l2.val)
{
m.next = l1;
l1 = l1.next;
}
else
{
m.next = l2;
l2 = l2.next;
}
m = m.next;
}
var l3 = l1 == null ? l2 : l1;
while (l3 != null)
{
m.next = l3;
l3 = l3.next;
m = m.next;
}
m.next = null;
return h;
}