Stacks versus Deques
We investigate the relative efficiency of a finite number of stacks in comparison to several variants of deques. In the nondeterministic setting, two stacks can simulate a general deque in linear time. This implies a negative answer to the question raised by Brandenburg whether a deque can simulate a finite number of tapes in linear time. Wealso show that in realtime an output-restricted deque cannot simulate two stacks for deterministic computations. It is known that a general deque can be simulated deterministically by three stacks in linear time. We describe an approach that is simpler to analyze and has a smaller constant factor (with respect to the required stack operations) than a previous solution.
KeywordsLinear Time Computing Machinery Green Item Deterministic Machine Push Operation
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