Google Docs HLD: Operational Transformation for Real-Time Co-Editing

Two people type into the same Google Doc at the same moment. Somehow neither one's cursor jumps, neither one's words get eaten, and a second later both screens show the identical document. That "somehow" is Operational Transformation (OT) — the algorithm that takes two edits made against the same starting text and rewrites them so they can be applied in any order and still land everyone on the same result. It's the quiet machinery behind Google Docs, and it's one of the most satisfying algorithms to derive from scratch in an interview. This is the inside of collaborative editing. The signature…