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发帖数: 318 | 1 Ponder This Challenge:
This is an old problem due to Roy Adler, Wayne Goodwyn and Benjamin Weiss
. To our knowledge, it remains unsolved.
We are given a collection of N cities and 2N one-way roads. (For example,
we are told that the two roads leading out of Pittsburgh lead to Buffalo
and Erie, respectively.) Each road leads from one city to another (or
possibly
back to the same city). Each city has exactly two roads leading out of it
, and at least one leading in. We are assured that it is possi |
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