Edit distance that also counts adjacent transpositions — one op instead of two for the classic teh → the typo.
The Damerau-Levenshtein distance is the minimum number of insertions, deletions, substitutions, and adjacent transpositions to turn one string into another. It counts ab → ba as one operation, matching how humans actually mistype. Standard Levenshtein counts the same swap as two (substitute + substitute).
This tool uses the optimal string alignment variant (a.k.a. restricted DL): each substring may be edited only once, so CA → ABC is 3 rather than the true DL distance of 2. That variant is O(mn) time and space, exactly matching the DP recurrence shown in the matrix.
Cell colouring: purple = cells on one optimal path; green = cells where a transposition was taken.