Flashback: A Reversible Bilateral Run-Peeling Decomposition of Strings
We introduce Flashback, a reversible string decomposition that repeatedly peels the maximal leading and trailing character runs from a sentinel-wrapped input, recording each pair as one bilateral token. Decomposition and reconstruction both run in O(n) time and space. Our central result is a run-pairing theorem: Flashback is equivalent to pairing the first run of the string with the last, the second with the second-to-last, and so on. This gives an exact token count of 1+[r/2] for a string with r maximal runs, and matches a lower bound that holds for any admissible bilateral run-peeling scheme. From the run-pairing theorem the main structural properties follow as corollaries: the irreduci...
| Authors | Thomas Konstantinovsky, Gur Yaari |
|---|---|
| Primary category | cs.DS |
| Published | 29 April 2026 |
| Last updated at source | 29 April 2026 |
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