LEETCODELOCK IN
Stop memorizing solutions. Learn how to think through every problem, pattern by pattern.
Given an array of integers nums and an integer target, return indices of the two numbers that add up to target.
Hash map
Store each complement as a key. One pass — look up before you insert.
O(n) time · O(n) space
Optimal. Single pass through the array, constant-time lookups.
Accepted
You arrived at the answer yourself.
That's what makes it stick.
How It Works
A system, not a
pile of problems.
Sliding window
Learn the Pattern
Before you touch a problem, you learn the framework behind it. Sliding window. Two pointers. Hash maps. Understand why each pattern exists and when to reach for it.
Two pointers
Solve with Guidance
Progressive hints move your thinking forward: broad to specific to concrete. You arrive at the answer yourself. That's what makes it actually stick.
Hash map
Master the Pattern
Track which patterns you've internalized. Problems stop feeling random and start feeling familiar. One pattern unlocks dozens of problems.
Talk through it like the real thing.
AI interviewer with a live transcript and an honest debrief at the end.
See the shape, then the problem.
Every problem mapped to its pattern. Recognize once, solve everywhere.
Don't lose what you learned.
Solved problems become flashcards. Review them right before they slip.
Hints that guide, not solve.
Vague nudge first, then the technique, then concrete code only if you really need it.
Why LeetLockin
Everything they do.
Plus what they skipped.
Pricing
Free to learn. Pro to master.
Start free. Upgrade when you want unlimited tutoring and mocks.
No credit card required
- Full curriculum (4 paths, 37 blocks)
- Full problem library (212+ problems)
- Python code editor + execution
- Progress tracking and streaks
- 5 AI tutor messages per week
Billed $59/year · cancel anytime
- Everything in Free
- Unlimited AI Socratic tutor
- Mock interviews with AI debrief
- Spaced-repetition flashcards from your solutions
- Streak freezes so a missed day doesn’t reset you
Cancel anytime from Settings. Curriculum stays free even after you cancel.
It’s time.
Stop memorizing.Lock in.
You don't need more problems. You need a better system.
Free to start · No credit card required