public static ListNode RemoveNthFromEnd(ListNode head, int n)
{
if (head == null) return head;
ListNode fast = head;
int visit = 0;
while (visit < n)
{
if (fast == null) break;
fast = fast.next;
visit++;
}
if (visit < n)
throw new ArgumentOutOfRangeException("n is too large");
// find the target node
ListNode prev = new ListNode(0);
prev.next = head;
ListNode slow = head;
while (fast != null)
{
slow = slow.next;
fast = fast.next;
prev = prev.next;
}
// delete
prev.next = slow.next;
return slow != head ? head : head.next;
}
private ListNode Reverse(ListNode head, ListNode reversed)
{
if (head == null) return reversed;
ListNode next = head.next;
head.next = reversed;
return Reverse(next, head);
}
public static void PrintLinkedList(ListNode head) {
while (head != null) {
Console.Write(head.val.ToString() + "->");
head = head.next;
}
Console.Write("NULL\n");
}
public ListNode DeleteDuplicates(ListNode head)
{
if (head == null || head.next == null)
return head;
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode prev = dummy;
ListNode curr = head;
while (curr != null)
{
// skip duplicates
while (curr.next != null && curr.next.val == curr.val)
curr = curr.next;
// delete
if (prev.next != curr)
{
prev.next = curr.next;
}
else
{ // curr is not duplicates
prev = prev.next;
}
curr = curr.next;
}
return dummy.next;
}
public ListNode RotateRight(ListNode head, int k)
{
if (head == null || k == 0) return head;
ListNode fake = new ListNode(0);
fake.next = head;
ListNode front = fake;
// get ending node and the total size
int i = 0;
while (front.next != null)
{
front = front.next;
i++;
}
k = k % i; // effective rotation number
// cut point
ListNode rear = fake;
for (int j = 0; j < i - k; j++)
{
rear = rear.next;
}
front.next = fake.next;
fake.next = rear.next;
rear.next = null;
return fake.next;
}
private int GetLength(ListNode head)
{
int len = 0;
while (head != null)
{
len++;
head = head.next;
}
return len;
}
//---------------------------------------------------------------------
// One pass method: make cycle
public ListNode GetIntersectionNode_M2(ListNode headA, ListNode headB)
{
ListNode A = headA;
ListNode B = headB;
while (A != B)
{
A = A == null ? headB : A.next;
B = B == null ? headA : B.next;
}
return A;
}
// Question #141
public static bool HasCycle(ListNode head)
{
ListNode slow = head;
ListNode fast = head;
while (fast != null && fast.next != null)
{
fast = fast.next.next;
slow = slow.next;
if (fast == slow)
return true;
}
return false;
}
// Iterative method
public ListNode MakeReverseIteration(ListNode head)
{
ListNode fake = null;
ListNode curr = head;
ListNode prev = fake;
while (curr != null)
{
ListNode next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
// #148
public ListNode SortLinkedList(ListNode head)
{
if (head == null || head.next == null) return head;
// find out mid point
ListNode fast = head.next.next;
ListNode slow = head;
while (fast != null && fast.next != null)
{
slow = slow.next;
fast = fast.next.next;
}
ListNode second = SortLinkedList(slow.next);
slow.next = null;
return Merge(SortLinkedList(head), second);
}
public ListNode MergeKLists(ListNode[] lists)
{
int N = lists.Length;
int start = 0;
int end = N - 1;
while (end > 0)
{
start = 0;
while (start < end)
{
// merger two lists
lists[start] = Merge2Lists(lists[start], lists[end]); // save result to start
start++;
end--;
}
}
return N > 0 ? lists[0] : null;
}
// Three passes method
public ListNode GetIntersectionNode_M1(ListNode headA, ListNode headB)
{
int lenA = GetLength(headA);
int lenB = GetLength(headB);
int diff = Math.Abs(lenA - lenB);
ListNode fast = lenB > lenA ? headB : headA;
ListNode slow = fast == headB ? headA : headB;
while (diff > 0)
{
fast = fast.next;
diff--;
}
while (fast != slow)
{
fast = fast.next;
slow = slow.next;
}
return fast;
}
private ListNode Merge2Lists(ListNode l1, ListNode l2)
{
ListNode fake = new ListNode(0);
ListNode curr = fake;
while (l1 != null && l2 != null)
{
if (l1.val < l2.val)
{
curr.next = l1;
l1 = l1.next;
}
else
{
curr.next = l2;
l2 = l2.next;
}
curr = curr.next;
}
ListNode r = l1 == null ? l2 : l1;
curr.next = r;
return fake.next;
}
// Question #142
public static ListNode DetectCycle(ListNode head)
{
ListNode fast = head;
ListNode slow = head;
while (fast != null && fast.next != null)
{
fast = fast.next.next;
slow = slow.next;
if (slow == fast)
{
break;
}
}
// no cycle
if (fast == null || fast.next == null) return null;
slow = head;
// meet at the cycle starting node
while (slow != fast)
{
slow = slow.next;
fast = fast.next;
}
return slow;
}
// merge two sorted list
private ListNode Merge(ListNode a, ListNode b)
{
ListNode dummy = new ListNode(0); // node before head
ListNode p = dummy;
while (a != null && b != null)
{
if (a.val < b.val)
{
p.next = a;
a = a.next;
}
else
{
p.next = b;
b = b.next;
}
p = p.next;
}
ListNode remain = a == null ? b : a;
p.next = remain;
ListNode head = dummy.next;
dummy = null;
return head;
}
//------------------------------------------------------------------
// Recursive method
public ListNode MakeReverseRecursion(ListNode head)
{
return Reverse(head, null);
}