Day 88 — Full mock interview day

mock day · 45-minute DSA · 45-minute system design · 30-minute behavioral

Tonight's goal: simulate the real loop with strict timing, spoken reasoning, and no breaks between rounds.

Tonight's protocol

Use the mock / mixed day protocol for the timed blocks. Use the revision-day protocol only when something fails the gate.

  1. 0:00-0:02: choose exactly one DSA problem and one system-design prompt from the menus below.
  2. 0:02-0:05: answer the warm-up MCQs. At minute 5, the DSA timer starts.
  3. 0:05-0:50 — DSA round: 0:05-0:07 say pattern, brute force, better approach, time, and space; 0:07-0:50 code without solution text. If stuck at 0:30, reread only the pattern name and restart your explanation.
  4. 0:50-1:35 — System-design round: no break. 0:50-1:00 requirements and scale; 1:00-1:10 API and data model; 1:10-1:25 boxes; 1:25-1:35 bottleneck and failure modes.
  5. 1:35-2:05 — Behavioral round: no break. 1:35-1:41 write conflict STAR, then 1:41-1:44 tell it; 1:44-1:50 write failure STAR, then 1:50-1:53 tell it; 1:53-1:59 write deep-dive STAR, then 1:59-2:02 tell it; 2:02-2:05 trim the longest answer.
  6. 2:05-2:10: score the self-check gate. Every miss gets one WA: <root cause> line.

The problem menu

Pick exactly one DSA row for the 45-minute coding round. Explain aloud before typing.

ProblemPattern nameSlot
Two Sum Hashing: the seen question 45 min
Product of Array Except Self Products without division 45 min
Longest Substring Without Repeating Characters Sliding Window I: the shrinking rule 45 min
Daily Temperatures Monotonic stack: whatever you pop found its answer 45 min
Reorder List Composing linked-list primitives 45 min
Diameter of Binary Tree Trees V: piggyback on height 45 min
Number of Islands Graphs I: flooding a grid 45 min
Coin Change DP III: fewest coins 45 min

Pick exactly one system-design prompt for the 45-minute design round.

PromptFocus
Scaling basicsscale up, scale out, CAP during partition
Cachingmisses, writes, eviction, freshness
Load balancingspread traffic across interchangeable servers
Database choicesreplication, sharding, indexes, access patterns
URL shortenerbase62 write path and cached redirect path
Rate limitertoken bucket versus sliding window
Chat systemfan-out, WebSockets, queues, delivery state

Warm-up MCQs

1. What must happen before any DSA code?

2. A learner codes silently, then explains after passing. What broke?

3. The DSA timer hits 25 stuck minutes. What now?

4. When does a failed DSA problem leave the queue?

5. Which DSA row enters the next revision list?

6. What does the behavioral block test?

Self-check gate

Pass bar

Failure path: add the failed DSA problem to the next revision list with WA: <missed invariant or bug>. Add the weakest system-design prompt with its missing step. Rewrite and retell any STAR story that crossed 3 minutes.