The 4-Week Interview Sprint

What each step gives you

1. Two Sum

   The sprint opens on the most familiar warm-up for a reason: one pass with a value-to-index hash map turns an O(n²) pair search into O(n), and the habit of asking what to remember while scanning returns all month. Solve it, then state both complexities aloud and check the duplicate case, exactly as you will need to in a real screen.

2. The Closing Gap: Two Pointers

   On a sorted array, a left and a right pointer close in from both ends, moving whichever side makes the sum too small or too large, so one pass replaces the double loop with no hash map at all. The pair_sum exercise is the base for Two Sum II, Container With Most Water and Valid Palindrome, and it sets up 3Sum at the end of the week.

3. Valid Parentheses

   Bracket matching with a stack: push openers, check each closer against the top, and require an empty stack at the end. In week one it adds the last-in, first-out pattern to your set, and it rewards a fast, clean solution because interviewers often use it as a warm-up before Min Stack, Decode String or evaluating an expression.

4. The Moving Frame: Sliding Window

   Find the best run of k consecutive numbers by adding the element that enters and subtracting the one that leaves, instead of re-summing every window. The fixed-window max_sum exercise is the first step toward the variable windows in Longest Substring Without Repeating Characters and Minimum Window Substring, where the window grows and shrinks under a condition.

5. 3Sum

   Find every unique triplet that sums to zero by sorting, fixing one number, and running two pointers over the rest while skipping duplicates at all three positions. It closes week one because it combines two patterns and punishes sloppy duplicate handling, which makes it a fair test of whether the week has stuck, with 3Sum Closest and 4Sum as natural follow-ups.

6. Binary Search: The Vault

   Week two starts with binary search, played as a vault you crack by halving a sorted window, then written as the exact loop against hidden tests. Push past the array version: the same template solves Koko Eating Bananas, Search in Rotated Sorted Array and minimum-capacity questions, where what is sorted is the space of possible answers.

7. BFS: The Flood

   Breadth-first search spreads from the start one ring at a time with a FIFO queue, so the first visit to any cell is its shortest distance on an unweighted grid, and the page races it against DFS to show why depth-first gives no such guarantee. Use the runnable code as your template for Rotting Oranges, Shortest Path in Binary Matrix and multi-source BFS problems.

8. Build Order: DFS & Topological Sort

   Depth-first search with white, gray and black colors finishes each task after everything it depends on, so reversing the finish order gives a build order, and meeting a gray node mid-recursion proves a cycle. That is the whole of Course Schedule I and II, and Kahn's in-degree queue, covered alongside, is worth having ready when the interviewer asks for a second method.

9. Dijkstra’s Shortest Paths

   Here you implement Dijkstra rather than watch it: tentative distances, the unsettled node with the smallest distance chosen next, relaxation along each outgoing edge, and -1 for anything unreachable. Passing the hidden tests prepares you for Network Delay Time, Path With Minimum Effort and cheapest-route variants, plus the questions about negative weights that usually follow.

10. The Loaded Bag: 0/1 Knapsack

    The 0/1 knapsack fills a table where each cell decides take it or leave it for one item at one capacity, then traces back to recover the choice. Writing the one-dimensional dp[c] version, sweeping capacity downward so each item is used once, prepares you for Partition Equal Subset Sum, Target Sum and Last Stone Weight II.

11. Fill the Grid, Walk It Back: Longest Common Subsequence

    LCS fills a grid where a match extends the diagonal and a mismatch takes the larger neighbor, then backtracks to recover the subsequence itself, the same idea diff tools use. The lcs_length exercise is the template for Edit Distance, Longest Palindromic Subsequence and Shortest Common Supersequence, the two-string table questions interviewers return to often.

12. LRU Cache

    Build a fixed-capacity cache that evicts the least recently used key, where get and put must both run in O(1), which forces you to pair a hash map with a doubly linked list or an ordered dictionary. It ends the coding weeks because it sits between coding and design, so expect follow-ups on thread safety, expiry times and how an LFU policy would differ.

13. The System Design Fundamentals Handbook

    Week three opens with the vocabulary the design round assumes: CAP and consistency models, concurrency and locking, partitioning and replication, consensus, stateless services and horizontal scaling, and back-of-the-envelope estimation. Read it until you can define each term in one sentence and name the trade-off it implies, because interviewers probe vocabulary through follow-up questions rather than direct ones.

14. Design a URL Shortener

    A full design built step by step: minting short codes with base62, choosing between 301 and 302 redirects, caching because reads dwarf writes, sharding billions of rows, and a queue for click analytics. Walk it once as a reader, then redo it on a blank page in 45 minutes as the candidate, since it is one of the most common warm-up prompts in design rounds.

15. 50 System Design Interview Questions

    Fifty questions with answers short enough to say aloud, across requirements, load balancing, caching, databases, consistency, messaging, reliability and design scenarios, opening with the four moves that structure a 45-minute round. Rehearse those moves on every prompt this week: clarify scope, estimate scale, sketch the architecture, then deep-dive the one or two components the constraints make interesting.

16. The Behavioral Interview Handbook

    Week four starts with what the behavioral round measures, the STAR structure with a worked example, and how to build a story bank that flexes across leadership, conflict, failure and ambiguity questions. Draft five or six stories and rehearse each to about two minutes, so that a prompt like tell me about a time you disagreed with your manager gets a specific answer rather than a generality.

17. The Resume & Portfolio Handbook

    Your resume has two readers, an applicant tracking system that scores keyword coverage against the job description and a human who skims for impact, and this handbook shows how to satisfy both, including scoring your resume the way the machine does. Update it now even with a loop booked: it frames the stories you tell, and any applications you send in parallel will need it.

18. The Salary Negotiation Handbook

    The last step covers the offer: why countering is almost always a positive expected-value bet, how your best alternative gives you leverage, why a higher starting number compounds, and how to actually make the ask. Prepare your numbers before the final round, because the question about your expectations often arrives before the offer does.