A similar question was asked earlier there, but the question here is the reverse of it, using two queues as a stack. The question...

Given two queues with their standard operations (enqueue, dequeue, isempty, size), implement a stack with its standard operations (pop, push, isempty, size).

There should be two versions of the solution.

  • Version A: The stack should be efficient when pushing an item; and
  • Version B: The stack should be efficient when popping an item.

I am interested in the algorithm more than any specific language implementations. However, I welcome solutions expressed in languages which I am familiar (,,,,,).

algorithm data-structures stack
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