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Editorial Team
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Asked: 2026-05-20T09:25:36+00:00

What algorithm to use to check if a given string matches one of set

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What algorithm to use to check if a given string matches one of set of prefixes, and which prefix from that set?

Other variation: given path and a set of directories, how to check if path is in one of set of directories (assuming that there are no symbolic links, or they do not matter)?

I’m interested in description or name of algorithm, or Perl module which solves this (or can be used to solve this).

Edit
Bonus points for solution which allow to effectively find ‘is prefix of’ relation between set of strings (set of directories)

For example, given set of directories: foo, foo/bar, foo/baz, quux, baz/quux, baz/quux/plugh the algorithm is to find that foo is prefix of foo/bar and foo/baz, and that baz/quux is prefix of baz/quux/plugh… hopefully without O(n^2) time.

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1 Answer

  1. Editorial Team

    The efficient way to do this would be using a Trie:

    http://en.wikipedia.org/wiki/Trie

    There is a package for it on CPAN:

    https://metacpan.org/pod/Tree::Trie

    (never used that package myself though)

    You need to consider your what operations need to be the most efficient. The lookup is very cheap in a Trie, but if you only build the trie for one lookup, it might not be the fastest way…

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