swerc2014 GREAT + SWERC = PORTO（dfs，注意姿势）

最新推荐文章于 2021-01-18 17:03:39 发布

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最新推荐文章于 2021-01-18 17:03:39 发布 · 1.1k 阅读

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博客讲述了作者在解决SWERC2014比赛中的一个问题时遇到的困难。原有的dfs策略是从左到右按列进行，但在遇到未出现过的字母时赋值并继续dfs，导致错误。正确的做法是先赋值一个字母，然后对所有字符串进行dfs检查可行性。如果可行则继续赋值下一个字母，直至所有字母都被赋值。错误在于返回时未能正确更新已赋值但不再成立的等式状态。

We want to have a great SWERC at Porto this year and we approached this challenge in several ways. We even framed it as a word addition problem, similar to the classic SEND+MORE=MONEY, where each letter stands for a single digit (0, 1, 2, ..., 8, 9) that makes the arithmetic operation correct. In word additions different letters cannot be assigned the same digit and the leftmost letter in a word cannot be zero (0). In particular, a single letter term cannot be zero.
GREAT + SWERC = PORTO
Given a word addition problem, compute the number of solutions (possibly zero).

Input