String search in constant space, linear time, for nonorderable alphabets.

In Rust terms this means we can define the function:

rust fn gs_find<T>(text: &[T], pattern: &[T]) -> Option<usize> where T: Eq { // ... }

and the function computes in O(n) time and O(1) space. In the worst case, this algorithm makes 4 n character comparisons.

Note that the Crochemore-Perrin (“Two Way” algorithm) is much superior if there is a linear order for the alphabet.

This work is Copyright 2017 by Ulrik Sverdrup "bluss"; see license terms in the package.

References

Both papers are recommended reading. The comments in this crate’s implementation are also meant to explain and point out important details, so that’s recommended reading too.

• [GS] Z. Galil and J. Seiferas, Time-Space-Optimal String Matching, Journal of Computer and System Sciences (1983)
• [CR] M. Crochemore and W. Rytter, Squares, Cubes, and Time-Space Efficient String Searching, Algorithmica (1995)
  • Crochemore-Rytter's description of the Galil-Seiferas algoritm has been very helpful and it explains how it works in concepts that we could implement.