Explaining the Aho-Corasick Algorithm
Franc0Fernand0 · x · 2026-07-10
The article reviews the Aho-Corasick string matching algorithm, proposed in 1975, which solved the scalability issue of repeatedly scanning documents for massive sets of keywords.
- Core Mechanism: Organizes keywords into a "prefix tree" and adds "failure pointers" (similar to the KMP algorithm) as shortcuts. When a match fails, it jumps directly, avoiding redundant checks.
- Efficiency Advantage: It only needs to read the target document once, reducing the time complexity to O(n + m + z) (where n is text length, m is total keyword length, and z is the number of matches). Search time is no longer affected by the number of keywords.
- Use Cases: This algorithm is still widely used today in the fgrep command, Intrusion Detection Systems (IDS), and DNA gene sequence search tools.
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