The learning platform
You’re not bad at codingYou just need stronger fundamentals
A browser-based project lab that teaches you data structures by building them from scratch, so technical interview prep finally starts to make sense.
- Learning-first. Free forever.
- Build real data structures from scratch
- Instant feedback in your browser
- Master DSA fundamentals before SWE interviews
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How it works
Learn it. Build it. Run it. Understand it.
Every module runs the same loop, so you always know what to do next.
Module 3 · Self-paced
Linked Lists
5 activities · ~140 min total
Nodes & pointers
Singly vs. doubly
LinkedList.append
Reverse a list
LRU cacheProject
42%
19 of 45 activities3 of 10 solved · Module 3Next: Reverse a list
linked_list.pytests.py
Python 3.11 · UTF-81class Node:
2 def __init__(self, value, next=None):
3 self.value = value
4 self.next = next
5
6class LinkedList:
7 def __init__(self):
8 self.head = None
9 self.size = 0
10
11 def append(self, value):
12 node = Node(value)
13 if self.head is None:
14 self.head = node
15 return
16 cur = self.head
17 while cur.next:
18 cur = cur.next
19 cur.next = node
20 self.size += 1
test_append_to_empty · ll.append(4); ll.head.value4 → 4
test_append_keeps_order · [1, 2, 3][1, 2, 3] → [1, 2, 3]
test_size_after_first_append · ll.append(4); ll.sizeexpected 1 · got 0
Hint: the early return on line 15 skips the size update. 6 more tests passed.
Curriculum
Fundamentals, then practice, then the interview
Not a list of problems to memorize. You implement each structure yourself, use it to solve the interview patterns built on top of it, then rehearse explaining it out loud.
- 01FundamentalsBuild the six core data structures from scratch.
- 02PracticeWeekly modules of interview patterns, problems and projects.
- 03Mock interviewsRehearse with a current FAANG engineer before the real one.
Phase 01 · Fundamentalsdata_structures/
Data structures from scratch
- 01ArrayListDynamic array: append, insert, remove, and resizing when it fills upTested
- 02LinkedListNodes and pointers: append, reverse, and the off-by-one trapsTested
- 03StackLIFO on top of your own list, with the empty-pop edge caseTested
- 04QueueFIFO enqueue and dequeue without the O(n) shiftTested
- 05HashTableHashing, buckets, collisions and load-factor resizingTested
- 06BinarySearchTreeInsert, search and traversals that every tree question assumesTested
Phase 02 · Practicemodules/ · one per week
Interview patterns, one module a week
- Week 1Arrays & Hashing
- Week 2Two Pointers & Sliding Window
- Week 3Graphs
- Week 4Trees & Tries
- Week 5Dynamic Programming
Free foreverLearning-first. The curriculum and problems don’t sit behind a paywall.
Nothing to installWrite and run code directly in the browser, with tests that run on submit.
Built for a laptopReadings and videos work on mobile. Coding problems open on desktop.
When the fundamentals are there, the interview is next
The platform gets you ready to be tested. Our services get you ready to be hired: mock interviews with current FAANG engineers, resume and LinkedIn rewrites, and full programs with the 60-Day Interview Guarantee.
Community
Don’t build alone
1,900+ aspiring and current software engineers learning and preparing together on Discord, with our team in the room.