Template: 2. TWO POINTERS — Same Direction (Fast/Slow)

2. TWO POINTERS — Same Direction (Fast/Slow)

# =============================================================================
# Use when: cycle detection, find middle, remove duplicates in-place
def fast_slow_pointers(head):
    slow = fast = head
    while fast and fast.next:
        slow = slow.next
        fast = fast.next.next
        if slow == fast:
            return True  # cycle detected
    return False  # slow is now at middle (if no cycle)


# =============================================================================