DAY 18 OF 30 · PATTERN PRACTICE
AI COACH90+ DSA PATTERNSMOCK INTERVIEWSSYSTEM DESIGNCODE PRACTICE
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Return the length of the longest substring with unique characters.
- Input
- "abba"
- Output
- 2
1def length_of_longest(s):2 left, seen = 0, {}3 for right, char in enumerate(s):4 left = last_seen[char]☺5 seen[char] = right☺ LINE 4
Keep left monotonic so the window never moves backward.
8.2/10
Communication82%
Problem solving88%
KEY MOMENT Recovered the edge case after execution exposed it.
PREPARING CANDIDATES FOR
Six stages.
One preparation system.
Build understanding, turn it into execution, and rehearse the real conversation. Every round of feedback points to the next useful practice.
- 01
- 02
- 03
- 04
- 05
- 06
01LEARN WITH DIRECTION
Structured learning paths
Choose a role, build the right foundations, and always know the next useful lesson instead of wandering through disconnected content.
- Role-specific routes across DSA, system design, PM, data science, and AI
- Theory, practice, revision, and animation in one path
- A saved resume point and clear next practice action
PATTERN 03 · LESSON 04 OF 07When should the window move?
Keep a valid range while each value enters and leaves at most once.
abbacdLEFTRIGHT
InvariantThe active window contains no repeated character.
02FOLLOW A COMPLETE PLAN
Two 90-day roadmaps
Choose the DSA Interview program or the AI, ML & LLM program, then work through one ordered day at a time with progress and a clear resume point.
- DSA Interview: DSA, system design, LLD/OOD, and behavioral
- AI, ML & LLM: machine learning, deep learning, data science, and AI system design
- Day-by-day theory, problems, mocks, progress, and certificates
DSA INTERVIEW ROADMAPDay 18 · Sliding window
18 / 90 DAYS20% complete
1213141516171819202122232425
✓
THEORYSliding-window invariantsRead · watch · visualize
12 min02
PROBLEMLongest substringCode · run · review
31 min03
MOCKExplain the trade-offLive voice follow-up
15 min03RECOGNIZE WHAT REPEATS
DSA patterns—and more
Build strong DSA pattern recognition first, then use the same structured sheet format across design, AI/ML, data science, and product interviews.
- 16 DSA patterns across 100 subpatterns, with visual mental models
- Dedicated sheets for system design, LLD/OOD, AI/ML, data science, and PM
- Company-wise questions connected to each pattern
DSASystem DesignLLD / OODAI / MLData SciencePM
PATTERN 17 · ARRAYS & STRINGSVariable-size sliding window
MEDIUM · 18 QUESTIONSConceptVisual modelQuestionsCompanies
abbacdLEFTRIGHT
Recognition cueLook for a contiguous range that must satisfy a changing condition.
01Grow Move right to include new values.02Repair Move left until the window is valid.03Measure Update the answer at each valid state.
04TURN INSIGHT INTO EXECUTION
AI code practice
Write and run a real solution, then ask the line-anchored coach for the smallest useful nudge without leaving your editor.
- Six-language editor with real execution
- ☺ line coach with escalating hints
- Sample, custom, and hidden test cases
- def length_of_longest(s):
- left, best = 0, 0
- last_seen = {}
- for right, char in enumerate(s):
- left = last_seen.get(char, 0)
- best = max(best, right-left+1)
LINE 5×
› is this right?
left can move backward here. Keep it monotonic with max(left, last_seen[char] + 1).ran your code · 2/3 passedTEST RESULTCASE 1CASE 2CASE 3
2/3 passedinput “abba” · expected 2 · received 3
05UNDERSTAND THE GAP
AI Coach, 1:1 tutoring
Choose how Ti teaches, talk through a difficult concept live, and watch explanations, diagrams, code, and notes take shape on the canvas.
- Live voice tutoring in five teaching styles
- Diagrams, code, math, and notes on canvas
- Transcript and session notes
SYSTEM DESIGNWhy put a token bucket at the edge?Ti is building this explanation live
01
Absorb short burstsTokens refill at a steady rate while valid bursts pass immediately.
CLIENTS→EDGE
BUCKET→API→STORErefill: 100 req/s · burst: 250
BUCKET→API→STORErefill: 100 req/s · burst: 250
NEXT CHECKWhere should counters live when regions fail independently?
TI IS SPEAKINGLooking at the canvas
NATURALSOCRATICFEYNMANFIRST PRINCIPLES
06REHEARSE UNDER PRESSURE
AI mock interviews
Enter a live voice round with the same working tools you use on the job, execute code when the round supports it, and review specific evidence afterward.
- Live voice technical and behavioral rounds
- Code Editor, Design Canvas, and Notes
- Executable DSA rounds with scores and key moments
class LRUCache:
def get(self, key):
node = self.cache.get(key)
self._move_to_front(node)
return node.valueEXECUTION5/5 TESTS PASSED42 ms · Python
THE FIRST ROUND SHOULD FEEL FAMILIAR
Your next interview should not be your first practice.
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Start practicingPRICING / PICK YOUR PACE
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- Support
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Focused preparation across selected paths
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- Learning paths
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- Full videos, editorials, infographics, and company kits
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All-track preparation with the highest practice allowance
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Own every path and both day-by-day roadmaps
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- AI practice
- 32 shared credits once · AI Coach or mock interviews
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- DSA Interview: DSA, system design, LLD/OOD, behavioral · AI, ML & LLM: ML, deep learning, data science, AI system design
- Pattern-first library
- Full videos, editorials, infographics, and company kits
- Access
- Both roadmap certificates · no monthly credit refill
See exact plan details
Starter: core learning with limited recurring practice.
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Elite: every live path and the highest recurring AI allowance.
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Preparation feels different when the path is clear.
See how engineers turn scattered preparation into clearer practice, stronger feedback loops, and more confident interviews.
LINKEDIN PROFILE01
“I spent thousands on interview coaching before finding thita.ai. The AI gives similarly detailed feedback, available instantly, at a fraction of the cost. The code review feature caught edge cases I always missed. This platform is seriously underpriced for what it offers.”
LINKEDIN PROFILE02
“With a full-time job and family, I could only study late nights. Unlike other platforms that require scheduling with peers, thita.ai's AI interviewer was always available. I practiced during my own hours and cleared my interviews after two months of consistent prep.”
LINKEDIN PROFILE03
“Unlike platforms where you just grind problems, thita.ai focuses on pattern recognition and problem-solving approaches. The AI explains the why behind solutions, not just the what. This helped me solve new problems I'd never seen before in my actual interviews.”
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“Honestly better than $300/hour interview prep sites. I've tried probably eight different platforms. thita.ai has the cleanest interface and smoothest experience. The code editor, real-time feedback panel, and session summaries make practicing enjoyable instead of a chore.”
LINKEDIN PROFILE05
“After each coaching session, thita.ai generates detailed notes with visual diagrams explaining my solution and alternatives. I've built an entire reference library from these notes. Reviewing them before interviews gave me clarity and confidence.”
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“As someone with five years of experience, most platforms felt too basic. thita.ai's AI quickly assessed my skill level and challenged me with appropriate problems, so I could go straight to what I actually needed to practice.”
LINKEDIN PROFILE07
“Before thita.ai, I was hopping between random YouTube videos and blog posts with no clear direction. This platform gave me structure and a roadmap. The organized content meant I wasn't wasting time on topics I already knew.”
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“I struggled with system design for months after passing DSA rounds at multiple companies. thita.ai's structured approach and instant feedback helped the patterns finally click. The AI coaching is like having a personal mentor available 24/7.”
LINKEDIN PROFILE09
“I've done mock interviews on Pramp and interviewing.io, but thita.ai's AI interviewer feels the most natural. It asks follow-up questions, challenges assumptions, and behaves like a real interview. That realism made me much more prepared.”
FIELD NOTES FOR THE INTERVIEW LOOP
03Notes for the next round.
01DSA PATTERNS · 8 MIN READ
The 16 DSA Patterns Behind 100 Subpatterns
Build pattern recognition before adding more problems to your queue.Read guide
02AI INTERVIEWS · 9 MIN READ
AI Interview Practice: Free Mock Interview Simulator
A practical guide to rehearsing technical rounds with useful feedback.Read guide
03RESUME NOTES · 10 MIN READ
Free ATS Resume Checker: Beat Applicant Tracking Systems
Understand what an ATS reads and make your experience easier to assess.Read guideQUESTIONS?
Plans, learning paths, AI practice, and access.
01LEARN02PLAN03RECOGNIZE04PRACTICE05COACH06REHEARSE
READINESS CONSOLEFeedback resolved
StrengthClear structure
GapFailure recovery
NextDistributed queues
NEXT PRACTICE →PEER PRACTICE / DISCORD
Prepare with people who are in the loop.
Share interview experiences, compare approaches, and get unstuck with engineers working toward the same next round.
01Find practice partnersCoordinate peer mocks across coding, design, data, AI, and product rounds.
02Review real approachesCompare trade-offs and learn how other candidates structure their answers.
03Stay accountableShare weekly goals, ask focused questions, and keep preparation moving.
Thita.ai is a technical-interview preparation platform for software engineering, system design, low-level design, data science, AI/ML and product management roles. It combines a 16-pattern-family DSA library (410 executable problems), live-voice AI mock interviews with structured feedback, an AI coach, system design and low-level design courses, and an AI resume analyser. 24,000+ engineers have used it. A free tier is available; paid plans start at $14.99/month (₹1,179/month in India, GST included), and one-time lifetime access to all learning content is ₹5,880 (US$69) plus 18% GST.