def isPalindromV2(head):
"""
:param head:
:return:
O(n) time, O(1) space
"""
if head is None or head.next is None:
return True
size = 0
ptr = head
while ptr:
size += 1
ptr = ptr.next
steps = size // 2
p1 = head
while True:
steps -= 1
if steps == 0:
break
p1 = p1.next
p2 = p1.next
if size % 2 != 0:
p2 = p2.next
p1.next = None
new_head = reverse_list(head)
while p2:
if p2.val != new_head.val:
return False
p2 = p2.next
new_head = new_head.next
return True
def isPalindrome(head):
"""
:type head: ListNode
:rtype: bool
O(n) time, O(n) space
"""
if head is None:
return True
vals = []
ptr = head
while ptr:
vals.append(ptr.val)
ptr = ptr.next
ptr = reverse_list(head)
idx = 0
while ptr:
if ptr.val != vals[idx]:
return False
ptr = ptr.next
idx += 1
return True
