// coding-interview-questions
Real coding questions, worked solutions, and the patterns behind them.
6 min read The join behaviors that trip up strong candidates: WHERE-versus-ON filtering, fan-out inflating aggregates, NULL traps in anti-joins, and self-joins. Read article
7 min read The ranking, framing, and ordering gotchas that separate people who have shipped SQL from people who memorized the syntax. Read article
6 min read Companies increasingly hand candidates a broken repo and a failing test instead of a blank editor, and the round rewards a very different skill than grinding LeetCode. Read article
6 min read Word Break looks like a string problem but rewards you for caching subproblems by start index, from the memoized recursion to the trie follow-up. Read article
5 min read The no-division array question rewards a prefix-and-suffix pass, and the O(1) space follow-up is where most candidates stumble. Read article
6 min read The two-pointer window that turns a quadratic substring scan into one linear pass, plus the stale-index guard that quietly breaks the fast version. Read article
5 min read The balanced-brackets question is a stack in disguise, and the same move carries straight into Min Stack and Decode String. Read article
5 min read Greedy returns the wrong coin count the moment denominations aren’t standard, so Coin Change needs a short dynamic-programming table instead. Read article
6 min read Course Schedule and its harder sibling are dressed-up cycle detection on a directed graph, and there are two clean ways to handle both. Read article
7 min read The grid-counting question turns up everywhere from Google to Citadel, and the part that gets scored is the follow-up, not the first solution. Read article
6 min read How sorting by start time turns merge intervals, insert interval, and meeting rooms into one linear sweep. Read article
6 min read The trapped-water problem has three standard solutions, and the gap between them is what an interviewer is actually grading. Read article
7 min read Why LeetCode 146 forces a hash map paired with a doubly linked list, how to code it cleanly, and where the LFU and TTL follow-ups go. Read article
6 min read Two Sum looks trivial, but the jump from the brute-force pair check to the one-pass hash map is the exact skill interviewers are screening for. Read article
7 min read A reference table mapping fifteen coding-interview patterns to the signal that triggers each one and the canonical problem to learn it on. Read article
What's missing, wrong, or worth adding? One line helps.
Sent — thank you. We read every one.
