Lesson 273
Aho-Corasick
Trie + Failure Links = Multi-Pattern Automaton
1:00How to match dozens or thousands of patterns in a single left-to-right pass over the text by building a trie augmented with BFS-computed failure links.
By the end, you can
- Explain why the naive k-pattern search is O(k * n) and how Aho-Corasick improves it.
- Build a trie for a small pattern set, identifying shared prefixes and endpoint nodes.
- Define a failure link and state what node it points to.
- Trace the BFS construction of failure links for a concrete trie.
- Identify the correct failure-link targets for specific nodes in the {he, she, his, hers} trie.
- Trace the single-pass scan of "ushers" through the automaton, noting failure-link jumps and output-link reports.
- Explain what output links do and why they are necessary for overlapping patterns.
- State the O(n + m + z) complexity and identify the real-world domains where Aho-Corasick is used.
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