Two-Pointer

# converging from both ends
left, right = 0, n - 1

while left < right:
    # process A[left] and A[right]

    if condition:
        left += 1
    else:
        right -= 1

# slow and fast pointers
slow = fast = start

while fast and fast.next:
    slow = slow.next
    fast = fast.next.next

    # detect cycle
    if slow == fast:
        break

# find cycle start or middle
slow = start
while slow != fast:
    slow = slow.next
    fast = fast.next

# variable window
left = 0

for right in range(n):
    # expand window: add A[right]

    while condition:
        # shrink window: remove A[left]
        left += 1

    # update result

# or fixed window
for right in range(n):
    if right >= k:
        # remove A[right - k]

    # add A[right]
    # update result