  This paper formulates the polar-code construction problem for the
successive-cancellation list (SCL) decoder as a maze-traversing game, which can
be solved by reinforcement learning techniques. The proposed method provides a
novel technique for polar-code construction that no longer depends on sorting
and selecting bit-channels by reliability. Instead, this technique decides
whether the input bits should be frozen in a purely sequential manner. The
equivalence of optimizing the polar-code construction for the SCL decoder under
this technique and maximizing the expected reward of traversing a maze is
drawn. Simulation results show that the standard polar-code constructions that
are designed for the successive-cancellation decoder are no longer optimal for
the SCL decoder with respect to the frame error rate. In contrast, the
simulations show that, with a reasonable amount of training, the game-based
construction method finds code constructions that have lower frame-error rate
for various code lengths and decoders compared to standard constructions.
