Reverse doubly linked list

Swap each node’s next and previous links, then make the old tail the head.

Remember: Swap both links; swap the ends.

Example: 10 ⇄ 20 ⇄ 30 becomes 30 ⇄ 20 ⇄ 10.

Time: O(n). Auxiliary space: O(1).

Formula: swap(current.next, current.prev)

Both next and prev links are rewired. The original tail becomes the new head.

Complexities describe the underlying algorithm; tutorial snapshots and rendering can use additional resources.

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