// 易错点：升序排序会导致逻辑完全错误（无法判断后车是否追前车）
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Англия — Премьер-лига|29-й тур
Россиянам станет тяжелее снять наличные08:49
Backtracking: everyone in the field knows that backtracking engines (PCRE, java, dotnet, javascript, PHP, ruby, python..) are bad because they are the poster child of denial of service attacks. O(2^n) match time complexity is not good. most backtracking implementations are a combination of clever optimizations duct taped to a very slow engine - for simple cases it works well, but using a pattern that is not affected by the optimizations, you get to see what the “real” worst-case behavior looks like.