---
title: 'Week 3'
description: 'Trees, heaps, and tries. Run the first scored mock. Open Track B and the pipeline.'
sidebar:
  icon: git-branch
---

**August 31 – September 6, 2026.** Finish trees. Add heaps and tries. Run the first scored system-design mock. Open Track B and the pipeline.

## Goals

- [ ] Finish trees. Learn heaps and tries.
- [ ] Run Mock #1 (premium, scored). Reach "lean hire" or better.
- [ ] Build the Stripe test-mode integration.
- [ ] Send 10 investor emails and 6 applications.

## Daily schedule

| Day | Concept — B1 (untimed) | Timed problems — B2 and B-set | Track B — B4 | Behavioral and pipeline — B5 |
|---|---|---|---|---|
| Mon | Trees: BST patterns | Subtree of Another Tree, Lowest Common Ancestor, Binary Tree Level Order, Right Side View, Count Good Nodes (5) + B-set | — | Send 10 investor emails |
| Tue | Trees: hard patterns | Validate BST, Kth Smallest in BST, Construct Tree from Preorder and Inorder (3) + B-set | **Mock #1** (premium) | Apply to Kraken |
| Wed | Heap (5 walkthroughs) | Kth Largest in a Stream, Last Stone Weight, K Closest Points, Kth Largest in an Array (4) + B-set | Build the Mock #1 fix list. Run a patch drill. | Apply to Anchorage, Paxos, and Brex |
| Thu | Heap depth and trie (2 walkthroughs) | Task Scheduler, Find Median from Data Stream; Implement Trie, Word Search II (intro) (4) + B-set | Track B 1: Stripe test-mode integration — payment intent, webhook, and idempotency | Apply to Ramp |
| Fri | Gate day. Do no new lesson. | 2 random mediums, plus review the Mock #1 result. | Review the gate result. | Write story 6: W3C and MIT influence |
| Sat | Buffer: redo red concepts | B-set catch-up: all due and overdue problems | Record all stories out loud, 90 seconds each | Apply to Robinhood |

## Daily blocks

Use the same 10-hour day as [Week 1](/schedule/week-1). Keep Sunday off.

:::tip
Book premium mocks in advance. Slots fill early.
:::

## Friday gate

:::warning[Gate]
Score Mock #1 at "lean hire" or better. Solve 2 random mediums at 8/10 or more. If you do not pass, repeat the week.
:::

## Outputs

- 16 A-set problems, timed.
- A heavy B-set week.
- Mock #1, scored, with a written fix list.
- The Stripe test-mode integration.
- 6 applications and 10 investor emails.