peekLast

peekLast is a non-destructive operation used on double-ended queues (deques). It returns the element at the back of the deque without removing it, providing a way to inspect the tail while leaving the structure intact. The method is commonly exposed in libraries and languages that implement deques, often alongside a corresponding peekFirst for the front end.

In terms of behavior, peekLast typically returns the last element or a value indicating that the deque is empty. In many implementations for Java, for example, the method returns null when the deque is empty. It is important to note that many standard deque implementations do not permit null elements, so a returned null is a reliable indicator of an empty structure rather than a stored null value. When operating in languages or libraries that support option types or exceptions, the exact return type and handling may differ.

Performance characteristics are usually straightforward: peekLast runs in constant time, O(1), since it only provides a view of the back element without modifying the deque.

Common use cases include inspecting the most recently added element, making decisions based on the tail without removal, or coordinating algorithms that examine both ends of a deque. Related operations include peekFirst (inspect the front), pollLast or removeLast (remove from the back), and their variants in the corresponding library’s API. In concurrent contexts, availability and safety of peekLast depend on the specific deque implementation.