def middle_node(self, head):
# write your code here
if not head:
return None
dummy = ListNode(-1)
dummy.next = head
slow, fast = dummy, dummy
while fast and fast.next:
slow = slow.next
fast = fast.next.next
return slow
def reverseBetween(self, head, m, n):
dummy = ListNode(-1, head)
mth_prev = self.findkth(dummy, m - 1)
mth = mth_prev.next
nth = self.findkth(dummy, n)
nth_next = nth.next
nth.next = None
self.reverse(mth)
mth_prev.next = nth
mth.next = nth_next
return dummy.next
def reorderList(self, head):
if head is None:
return head
#find mid
slow = head
fast = head
while fast.next and fast.next.next:
slow = slow.next
fast = fast.next.next
mid = slow
#cut in the mid
left = head
right = mid.next
if right is None:
return head
mid.next = None
#reverse right half
cursor = right.next
right.next = None
while cursor:
next = cursor.next
cursor.next = right
right = cursor
cursor = next
#merge left and right
dummy = ListNode(0)
while left or right:
if left is not None:
dummy.next = left
left = left.next
dummy = dummy.next
if right is not None:
dummy.next = right
right = right.next
dummy = dummy.next
return head
def reverseBetween(self, head, m, n):
diff, dummy, cur = n - m + 1, ListNode(-1), head
dummy.next = head
last_unswapped = dummy
while cur and m > 1:
cur, last_unswapped, m = cur.__next__, cur, m - 1
prev, first_swapped = last_unswapped, cur
while cur and diff > 0:
cur.next, prev, cur, diff = prev, cur, cur.next, diff - 1
last_unswapped.next, first_swapped.next = prev, cur
return dummy.__next__
def reorderList(self, head):
if head == None or head.next == None:
return head
fast, slow, prev = head, head, None
while fast != None and fast.next != None:
fast, slow, prev = fast.next.next, slow.next, slow
current, prev.next, prev = slow, None, None
while current != None:
current.next, prev, current = prev, current, current.next
l1, l2 = head, prev
dummy = ListNode(0)
current = dummy
while l1 != None and l2 != None:
current.next, current, l1 = l1, l1, l1.next
current.next, current, l2 = l2, l2, l2.next
return dummy.next
def reverseBetween(self, head, m, n):
dummyNode = ListNode(0)
p = dummyNode
q = head
for x in range(m - 1):
p.next = q
q = q.next
p = p.next
start = None
end = q
next = None
for x in range(m, n + 1):
next = q.next
q.next = start
start = q
q = next
p.next = start
end.next = next
return dummyNode.next
def __init__(self):
self.dummy = self.tail = ListNode(-1)
def push(self, x):
node = ListNode(x)
node.pre = self.tail
self.tail.nxt = node
self.tail = node