Last active
February 5, 2022 20:02
-
-
Save xpqz/c19ca3ef97b5437761cad3925ba5388c to your computer and use it in GitHub Desktop.
Manacher's algorithm for finding the longest palindromic substring in Dyalog APL (⎕IO←0)
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| ∇ res←manacher str;S;c;r;radii;i;ir | |
| c r radii←0 0 (0↑⍨≢S←'|',∊'|',⍨⍪str) | |
| :for i :in ⍳≢S | |
| radii[i]←{r>i:radii[(2×c)-i]⌊r-i⋄0}⍬ | |
| :trap 3 ⍝ Catch index errors if the below goes out of bounds | |
| :while =/S[i(+,-)1+i⊃radii] | |
| radii[i]+←1 | |
| :endwhile | |
| :endtrap | |
| :if r<ir←i+i⊃radii | |
| c r←i ir | |
| :endif | |
| :endfor | |
| c←radii⍳r←⌈/radii | |
| res←S[c(+(⊢+∘⍳1+-)-)r]~'|' | |
| ∇ |
Author
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Passable tradfn implementation of Manacher's algorithm (https://en.wikipedia.org/wiki/Longest_palindromic_substring)