def reverse_k(L, k):
dummy_head = ListNode(0, L)
sublist_predecessor = dummy_head
sublist_head = dummy_head.next
sublist_successor = dummy_head
sublist_tail = dummy_head.next
while sublist_head:
# Identify the tail of sublist of k nodes to be reversed.
num_remaining = k
while num_remaining:
sublist_successor = sublist_tail
sublist_tail = sublist_tail.next
num_remaining -= 1
if not sublist_tail:
break
if num_remaining > 0:
# Specification says not to reverse.
return dummy_head.next
sublist_successor.next = None
reverse_linked_list(sublist_head)
# Splice the reversed sublist.
sublist_predecessor.next = sublist_successor
# Go on to the head of next sublist.
sublist_predecessor = sublist_head
sublist_head.next = sublist_tail
sublist_head = sublist_tail
sublist_successor = None
return dummy_head.next
def is_linked_list_a_palindrome(L):
slow = fast = L
while fast and fast.next:
fast, slow = fast.next.next, slow.next
first_half_iter, second_half_iter = L, reverse_linked_list(slow)
while second_half_iter and first_half_iter:
if second_half_iter.data != first_half_iter.data:
return False
second_half_iter, first_half_iter = (second_half_iter.next,
first_half_iter.next)
return True
def is_linked_list_a_palindrome(L):
# Finds the second half of L.
slow = fast = L
while fast and fast.next:
fast, slow = fast.next.next, slow.next
# Compares the first half and the reversed second half lists.
first_half_iter, second_half_iter = L, reverse_linked_list(slow)
while second_half_iter and first_half_iter:
if second_half_iter.data != first_half_iter.data:
return False
second_half_iter, first_half_iter = (second_half_iter.next,
first_half_iter.next)
return True
def is_linked_list_a_palindrome(L):
# Finds the second half of L.
slow = fast = L
while fast and fast.next:
fast, slow = fast.next.next, slow.next
# Compares the first half and the reversed second half lists.
first_half_iter, second_half_iter = L, reverse_linked_list(slow)
while second_half_iter and first_half_iter:
if second_half_iter.data != first_half_iter.data:
return False
second_half_iter, first_half_iter = (second_half_iter.next,
first_half_iter.next)
return True
def zipping_linked_list(L):
if not L or not L.next:
return L
# Finds the second half of L.
slow = fast = L
while fast and fast.next:
slow, fast = slow.next, fast.next.next
first_half_head = L
second_half_head = slow.next
slow.next = None # Splits the list into two lists.
second_half_head = reverse_linked_list(second_half_head)
# Interleave the first half and the reversed of the second half.
first_half_iter, second_half_iter = first_half_head, second_half_head
while second_half_iter:
second_half_iter.next, first_half_iter.next, second_half_iter = (
first_half_iter.next, second_half_iter, second_half_iter.next)
first_half_iter = first_half_iter.next.next
return first_half_head
def zipping_linked_list(L):
if not L or not L.next:
return L
# Finds the second half of L.
slow = fast = L
while fast and fast.next:
slow, fast = slow.next, fast.next.next
first_half_head = L
second_half_head = slow.next
slow.next = None # Splits the list into two lists.
second_half_head = reverse_linked_list(second_half_head)
# Interleave the first half and the reversed of the second half.
first_half_iter, second_half_iter = first_half_head, second_half_head
while second_half_iter:
second_half_iter.next, first_half_iter.next, second_half_iter = (
first_half_iter.next, second_half_iter, second_half_iter.next)
first_half_iter = first_half_iter.next.next
return first_half_head
