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Longest Common Subsequence (LCS) and the 2D DP family.

LCS is the template 2D-sequence DP behind diff tools and bioinformatics. Interviewers look for rebuilding the match/mismatch recurrence from memory and not mixing up subsequence (gaps allowed) with substring (contiguous). The answer follows.

Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.

LCS is the template 2D-sequence DP behind diff tools and bioinformatics. Interviewers look for rebuilding the match/mismatch recurrence from memory and not mixing up subsequence (gaps allowed) with substring (contiguous). The answer follows.

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