Junior
Land your first or second engineering job. Build pattern recognition for the easy/medium-easy problems that dominate junior loops, learn the Big O basics, and tell good stories about learning and ownership.
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The handful of patterns that cover ~70% of junior coding screens.
Two Pointers
Two indices walk a sorted (or paired) structure from different positions to converge on a target.
Sliding Window
Maintain a window of elements over a sequence; expand/shrink to satisfy a constraint while tracking an aggregate.
Tree BFS
Level-order traversal using a queue; emit one level at a time.
Tree DFS
Recursive or stack-based depth-first traversal; pre/in/post order.
Fast & Slow Pointers (Floyd's)
Two pointers move at different speeds through a linked structure to detect cycles or find midpoints.
In-Place Reversal of LinkedList
Reverse pointers segment by segment without extra space using prev/curr/next bookkeeping.
Classic easy problems. Type them, recognize them, solve them in your sleep.
Solve these
Two Sum
easy · blind75
Valid Anagram
easy · blind75
Contains Duplicate
easy · blind75
First Unique Character in a String
easy · neetcode150
Valid Palindrome
easy · neetcode150
Linked List Cycle
easy · blind75
Maximum Depth of Binary Tree
easy · blind75
Reverse Linked List
easy · blind75
Best Time to Buy and Sell Stock
easy · blind75
Climbing Stairs
easy · blind75
Maximum Subarray
easy · blind75
Reverse String
easy · neetcode150
Move Zeroes
easy · neetcode150
Squares of a Sorted Array
easy · neetcode150
Fizz Buzz
easy · neetcode150
Know O(1), O(log n), O(n), O(n log n), and O(n²) cold. Recognize them in code.
Open Big O Quiz
Time complexity of accessing the element at a known index in an array?
Answer: O(1)
Average time complexity of inserting a key/value into a hash map?
Answer: O(1)
Average time complexity of looking up a key in a hash map?
Answer: O(1)
Time complexity of binary search on a sorted array of n elements?
Answer: O(log n)
Search in a balanced binary search tree of n nodes?
Answer: O(log n)
Time complexity of merge sort on n elements?
Answer: O(n log n)
Worst-case time complexity of linear search through an unsorted array?
Answer: O(n)
Time complexity of the naive recursive Fibonacci (no memoization)?
Answer: O(2^n)
Time complexity of Fibonacci with memoization?
Answer: O(n)
Time complexity of a sliding window pass over an array of n elements?
Answer: O(n)
Time complexity of a two-pointer sweep over a sorted array of n elements?
Answer: O(n)
Time complexity of visiting every cell of an n by m matrix once?
Answer: O(n * m)
The handful of systems concepts that come up even at junior interviews — vanilla mutex, basic indexes, normalization.
Open Systems quiz
Mutex / Lock
Mutual-exclusion primitive: at most one thread holds the lock at a time, serializing access to a critical section.
Semaphore
Counter with atomic acquire/release: lets at most N permits be held simultaneously. Generalizes the mutex (N=1).
B-tree / B+tree Index
Balanced, fan-out heavy tree where leaves hold sorted keys (and in B+trees, are linked for range scans). Lookup, insert, delete in O(log n).
Hash Index
Hash table over a column; O(1) average point lookup, but no order, so no range scans or ORDER BY.
Read code + a failing test, find the bug. Off-by-one, missing edge cases, default mutable args.
Practice debugging
JOINs, GROUP BY, NULL handling — the queries you'll write on day one.
Practice SQL
Password storage, basic XSS / SQL injection, input validation — the bare minimum every junior must know.
Practice security
Junior interviews probe curiosity, learning ability, and ownership of small things — not strategy.
Practice these
Tell me about a time you had to learn a new technology, language, or tool quickly for a project.
Learning & Growth
Walk me through the first time you had to make a change in a large codebase you didn't write.
Learning & Growth
Tell me about a time you were stuck on a task. How did you decide when to keep trying versus ask for help?
Asking for Help
Tell me about a piece of code review feedback that was hard to take. What did you do with it?
Receiving Feedback
Describe a time you worked closely with a more senior engineer. What did you take away from it?
Teamwork
Tell me about the first real bug you fixed in production code. Walk me through how you tracked it down.
Ownership
Tell me about the first feature you shipped end-to-end. What did you own?
Ownership
Tell me about a time you had to explain something technical to a non-technical teammate (PM, designer, support).
Communication
Describe a time you committed to something in standup and realized partway through the day you weren't going to finish.
Time Management
Tell me about a time you went looking into something nobody asked you to investigate — a weird log, an unexplained metric, a flaky test.
Curiosity