def reverseBetween(self, head, m, n):
"""
:type head: ListNode
:type m: int
:type n: int
:rtype: ListNode
"""
if head is None or head.next is None or m == n:
return head
headnode = ListNode(-1)
headnode.next = head
anchor = headnode
for _ in range(m - 1):
anchor = anchor.next
a = anchor.next
b = a.next
c = b.next
k = n - m
for _ in range(k):
b.next = a
if c:
a, b, c = b, c, c.next
else:
a, b = b, c
anchor.next.next = b
anchor.next = a
return headnode.next
def addAtHead(self, val):
"""
Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.
:type val: int
:rtype: void
"""
newnode = ListNode(val)
newnode.next, self.headnode.next = self.headnode.next, newnode
if self.length == 0:
self.tail = newnode
self.length += 1
def deleteDuplicates(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
headnode = ListNode(None)
headnode.next = head
delete = False
p = headnode # prev
c = head # current
while c:
while c.next and c.val == c.next.val:
c.next = c.next.next
if not delete:
delete = True
if delete:
c = c.next
p.next = c
delete = False
else:
c = c.next
p = p.next
return headnode.next
def addAtIndex(self, index, val):
"""
Add a node of value val before the index-th node in the linked list.
If index equals to the length of linked list, the node will be appended to the end of linked list.
If index is greater than the length, the node will not be inserted.
:type index: int
:type val: int
:rtype: void
"""
if index < 0 or index > self.length:
return None
if index == 0:
self.addAtHead(val)
elif index == self.length:
self.addAtTail(val)
else:
insert_point = self._get(index)
newnode = ListNode(insert_point.val)
newnode.next = insert_point.next
insert_point.next = newnode
insert_point.val = val
self.length += 1
if insert_point is self.tail:
self.tail = insert_point.next