为什么双向算法反向匹配左侧部分？

Question

Two Way算法是子字符串搜索算法(primary paper, 1.4 MB PDF)。

它将搜索模式 x 分成两部分： x = x _l x _r ，首先它尝试将 x _r 与文本匹配，如果成功，则算法规定匹配 x _l in反向（即从右到左的顺序）。

• 为什么 x _l 从右到左匹配？
• 我可以用左右比较代替吗？

问题的原因很简单：订单未指定的比较已经可用并且可能更高效，请考虑优化的memcmp或展开的循环。

Answer 1

From an efficiency point of view it obviously doesn't matter. The only other reason I can think of is: in case of non-matching, a right-to-left attempt potentially leaves the algorithm with more information about a partial match. So going RTL, if we match 2 characters in xl and then fail, we know we have a partial, contiguous match of 2 chars + xr. If we match xl LTR and fail, we know nothing more than the xr match.