2d dp

Edit distance is the canonical 2D string DP, behind spell-check, diff, and fuzzy matching. The signal is defining the subproblem and the insert/delete/replace recurrence. Here is the answer.

LCS is the template 2D-sequence DP behind diff tools and bioinformatics. The signal is reconstructing the match/mismatch recurrence cold and not confusing subsequence (gaps allowed) with substring (contiguous). Here is the answer.

The canonical grid DP where each cell depends on three neighbors at once. The signal interviewers want is the min-of-three recurrence, and the reason it has to be min. Here is the answer.