Patternwise

DSA · LLD · HLD · AI · Interviews

Learn the pattern.
Pass the loop.

Patternwise teaches engineering interviews the way they actually work: recognise the pattern, understand why it's fast, practise it on a ladder, then defend it in a mock interview that doesn't go easy on you.

Start with DSA patterns See the 8-week plan

What do you want to master?

Six tracks. One loop.

0118 patterns · 143 problems

DSA by pattern

18 patterns, each with an analogy, a step-through visualizer and an easy → hard ladder.

Two pointersSliding windowGraphsDP
Open
0241 lessons · 20 problems

Low-level design

OOP, SOLID and the design patterns that matter, then classic machine-coding problems.

SOLIDPatternsConcurrency
Open
0346 lessons · 22 problems

System design

From DNS to multi-region: caching, sharding, queues, consensus — then full design walkthroughs.

CachingShardingKafkaCAP
Open
0449 lessons · 10 projects

AI engineering

Transformers to production: RAG, agents, MCP, LangGraph, evals, guardrails and serving.

RAGAgentsMCPEvals
Open
058 weeks · 6 rounds

Interview prep

An 8-week plan, a playbook for every round and the frameworks to use in the room.

PlanBehaviouralFrameworks
Open
06Pass / Fail · scored /100

Mock interview

An AI interviewer that asks one question at a time, probes your gaps and grades you honestly.

Resume-aware6 rounds
Open

See it run

Don't memorise code. Watch it think.

Every pattern has a visualizer like this one. Press play, step with the arrow keys, or type your own input.

Visualize

Longest substring without repeating characters

Given a string, find the length of the longest substring with all-unique characters.

0
a
1
b
2
c
3
a
4
b
5
c
6
b
7
b
8
x
9
y
10
z

seen (char → last index)

{}
01/34

Window is empty. It will only ever grow on the right and shrink on the left.

pythonline 3
1def longest_unique(s):2    seen = {}            # char -> last index3    left = best = 04    for right, ch in enumerate(s):5        if ch in seen and seen[ch] >= left:6            left = seen[ch] + 1   # jump past the duplicate7        seen[ch] = right8        best = max(best, right - left + 1)9    return best

variables

left
0
best
0
Browse all 18 patterns

How it works

Learn → Practise → Defend.

  1. 01

    Learn

    Structured tracks, ordered by prerequisite. Plain-English explanations first, jargon second.

  2. 02

    Practise

    Pattern ladders, LLD problems and system-design case studies with a timer and a hidden reference answer.

  3. 03

    Defend

    Run a mock interview on what you just learned. The AI probes, doesn't hint, and grades out of 100.

Mock interviews

It behaves like an interviewer, not a tutor.

Pick a topic and round, optionally upload your resume. One question at a time, follow-ups when you're vague, and a report that quotes your own answers. 55 and above is a pass.

85+
Excellent
70
Good
55
Adequate
<55
Weak
Start an interview

Ready when you are.

Pattern #1: Two Pointers