Learn the vocabulary of matching thousands of patterns against text in a single linear pass.
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1 / 5
A teammate explains that a text-scanning algorithm builds a trie of many search patterns augmented with failure links, so it can find every occurrence of every pattern in a single linear pass over the text, rather than rescanning for each pattern separately. What algorithm is being described?
The Aho-Corasick algorithm is exactly this: it builds a trie of all search patterns augmented with failure links, similar in spirit to the KMP failure function but generalized across many patterns, so a single linear scan of the text reports every occurrence of every pattern. A hash collision is an unrelated hash-table concept about two keys sharing a bucket. This single-pass-many-patterns approach is exactly why Aho-Corasick is the standard choice for multi-pattern text scanning, such as antivirus signature matching.
2 / 5
During a design review, the team adopts Aho-Corasick for a content filter that must check incoming text against thousands of banned phrases, specifically so the whole text is scanned once instead of once per banned phrase. Which capability does this provide?
Aho-Corasick here provides linear-time multi-pattern matching regardless of how many patterns are searched for, since the trie and failure links let one pass over the text find all matches. Running a separate single-pattern search once per banned phrase means total scanning time grows with the number of phrases, which becomes far too slow once thousands of phrases are involved. This one-pass-for-all-patterns behavior is exactly why Aho-Corasick is favored for large-scale multi-pattern text filtering.
3 / 5
In a code review, a dev notices a content filter loops over a list of a thousand banned phrases and reruns a separate single-pattern substring search for each one against the same input text. What does this represent?
This is a missed Aho-Corasick opportunity, since building one trie with failure links for all thousand phrases would find every match in a single linear pass instead of a thousand separate scans. A cache eviction policy is an unrelated concept about discarded cache entries. This thousand-separate-scans pattern is exactly the kind of avoidable cost a reviewer flags once many patterns must be matched against the same text.
4 / 5
An incident report shows the content filter's latency grew linearly with the number of banned phrases, causing timeouts once the list passed a few thousand entries, because each phrase triggered its own separate scan of the input text. What practice would prevent this?
Building a single Aho-Corasick automaton over all banned phrases lets one linear pass over the input text find every match regardless of how many phrases exist. Continuing to rerun a separate single-pattern scan for every banned phrase regardless of how many phrases the list contains is exactly what caused the growing latency and timeouts described in this incident. This one-pass-multi-pattern approach is the standard fix once scanning cost is confirmed to grow with the number of patterns.
5 / 5
During a PR review, a teammate asks why the team reaches for Aho-Corasick instead of just calling a single-pattern search function once per banned phrase, given that the single-pattern function is already implemented and well tested. What is the reasoning?
Aho-Corasick trades some upfront trie-construction cost for a single linear pass that scales independently of the number of patterns, while repeating a single-pattern search is simpler to reuse but makes total scanning time grow with the pattern count. This is exactly why Aho-Corasick is favored once many patterns must be matched against the same text, while repeating a single-pattern search remains acceptable for just one or two patterns.