def rearrange_linked_list(self, head: ListNode) -> ListNode:
# find middle of the linked list
slow, fast = head, head
head_backup = head
prev = slow
while fast and fast.next:
prev = slow
slow = slow.next
fast = fast.next.next
#print(slow.val)
# reverse second half of the linked list
rev_head = self.reverse_linked_list(slow)
#print(rev_head.val)
prev.next = None
# rearrange the linked list
while head and rev_head:
head_next = head.next
rev_head_next = rev_head.next
head.next = rev_head
rev_head.next = head_next
head = head_next
rev_head = rev_head_next
# return head of linked list
return head_backup
def reverse_linked_list(self, head: ListNode) -> ListNode:
prev = None
while head:
_next = head.next
head.next = prev
prev = head
head = _next
return prev
def partition(self, head, x):
# write your code here
dummy = ListNode(0)
dummy.next = head
pre = insert_node = dummy
while head:
if head.val < x:
if insert_node.next != head:
pre.next = head.next
node = insert_node.next
insert_node.next = head
head.next = node
head = pre.next
insert_node = insert_node.next
else:
insert_node = head
pre = head
head = head.next
else:
pre = head
head = head.next
return dummy.next