Week 12 · Day 3 · 2026-10-14 WED · MOCK A
Unseen mock A: incident truth platform
Exact Daily Blocks
Run a realistic unknown-system mock focused on operational truth, derived dashboards, verification, and recovery.
| 08:50-10:55 | System design 45-minute adaptive mock: design a customer incident truth and remediation platform that merges deploys, alerts, tickets, ownership, customer impact, and post-incident verification. |
|---|---|
| 14:30-16:15 | NeetCode Backtracking Exactly three unique slots; each is 30m solve + 5m evidence. |
| 20:30-21:15 | Recall / mock repair Debrief the mock and repair one incorrect source-of-truth/derived-data boundary. |
DDIA decision links
Only exact Ch13/Ch14 sections that change Week 12 decisions are linked.
| Decision question | Exact DDIA section | Design consequence |
|---|---|---|
| Mock A: where must correctness live in an incident-truth system? | Ch13 - 数据库的端到端原则 | Incident correctness is checked at workflow and reconciliation boundaries, not delegated to a single queue, dashboard, or database. |
| Mock A: how does the system remain reviewable after a wrong derived incident state? | Ch13 - 为可审计性而设计 | All derived incident decisions carry provenance, actor, model/rule version if any, and correction history. |
Algorithm block
Diagnostic decision: select Backtracking, not a weakest prior tag, because no production scorecard records a weaker tag and final week needs recursive state-space pruning under pressure.
| Slot | Problem | Pattern | Invariant | Bug risk | Time | Space |
|---|---|---|---|---|---|---|
| 7 | Permutations II NEW · Backtracking · 30m solve + 5m evidence | sorted used-set duplicate control | Equal value can be used only after its previous twin is used at this depth order. | Wrong duplicate condition with used[i-1]. | O(n n!) | O(n) stack + output |
| 8 | Word Search NEW · Backtracking · 30m solve + 5m evidence | grid DFS with visited marks | A cell is used once per path and restored on return. | Leaking visited state across starts. | O(mn 4^L) | O(L) stack |
| 9 | Letter Combinations of a Phone Number NEW · Backtracking · 30m solve + 5m evidence | cartesian DFS | Depth equals processed digit count. | Returning [""] for empty input. | O(4^n n) | O(n) stack + output |
Output
| Deliverable | Mock A score, two deep dives, hard-fail check, and one repaired answer. |
|---|---|
| Artifacts | 30-project map Chinese synthesis Synthesis audio English recall Recall PDF Weak repair Repair audio Cohort crosswalk Mock A contract |
Detailed lecture notes, audio, recall scripts, PDFs, Staff Q&A, and mock packs are archived locally and are intentionally not published on this site.