public static bool IsPalindrome(ListNode head)
{
if (head == null || head.next == null)
{
return true;
}
tempHead = head;
return IsPalin(head);
}
public static ListNode merge(ListNode l1, ListNode l2)
{
ListNode l = new ListNode(0), p = l;
while (l1 != null && l2 != null)
{
if (l1.val < l2.val)
{
p.next = l1;
l1 = l1.next;
}
else
{
p.next = l2;
l2 = l2.next;
}
p = p.next;
}
if (l1 != null)
p.next = l1;
if (l2 != null)
p.next = l2;
return l.next;
}
private static void TestCases()
{
//QuickSort(new int[] { 2, 5, 1, 6, 7, 4 });
//SummaryRanges(new int[] { 0, 1, 2, 4, 5, 7, 8 });
//ThreeSum(new int[] { -1, 0, 1, 2, -1, -4 });
//LargestNumber(new int[] { 3, 30, 34, 5, 9 });
//int ele = FindKthLargest(new int[] { 2, 5, 1, 6, 7, 4 }, 3);
ListNode head = new ListNode(1);
ListNode p = head;
p.next = new ListNode(2);
for (int i = 2; i <= 3; i++)
{
p.next = new ListNode(i);
p = p.next;
}
p.next = new ListNode(2);
p = p.next;
p.next = new ListNode(1);
IsPalindrome(head);
ListNode q = head;
q = q.next;
double x = Math.Pow(3, 2);
}
private static bool IsPalin(ListNode head)
{
//current node is the last one
if (head.next == null)
{
return head.val == tempHead.val;
}
//when return true, head is the last second one
bool res = IsPalin(head.next);
tempHead = tempHead.next;
return res && head.val == tempHead.val;
}
public static ListNode sortList(ListNode head)
{
if (head == null || head.next == null)
return head;
// step 1. cut the list to two halves
ListNode prev = null, slow = head, fast = head;
while (fast != null && fast.next != null)
{
prev = slow;
slow = slow.next;
fast = fast.next.next;
}
prev.next = null;
// step 2. sort each half
ListNode l1 = sortList(head);
ListNode l2 = sortList(slow);
// step 3. merge l1 and l2
return merge(l1, l2);
}
public static void ReorderList(ListNode head)
{
ListNode lN = head;
ListNode fast = head;
ListNode slow = head;
ListNode pre = null;
while (fast != null && fast.next != null)
{
pre = slow;
slow = slow.next;
fast = fast.next.next;
}
//reverse from slow to fast
ListNode dummy = null;
ListNode cur = slow;
while (cur != null)
{
ListNode next = cur.next;
cur.next = dummy;
dummy = cur;
cur = next;
}
//merge two part of link list
ListNode rN = dummy;
ListNode newHead = lN;
while (lN != null)
{
ListNode lnNext = lN.next;
ListNode rnNext = rN.next;
lN.next = rN;
//left part to the end, then right part just leave it as it
if (lnNext == null)
{
break;
}
rN.next = lnNext;
lN = lnNext;
rN = rnNext;
}
}
