Longest Word in Dictionary
A medium-tier problem at 53% community acceptance, tagged with Array, Hash Table, String. Reported in interviews at Pinterest and 0 others.
Longest Word in Dictionary shows up on Pinterest assessments and it's exactly the kind of problem that blindsides candidates who haven't thought about build-order carefully. You're given an array of strings and need to find the longest word you can construct by using letters from other words in the array. The catch: order matters. You can't just grab the longest string. Most candidates start greedy and fail. This is where StealthCoder becomes your safety net if the pattern doesn't click during your live OA.
Companies that ask "Longest Word in Dictionary"
Longest Word in Dictionary is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too.
Get StealthCoderThe real trick is understanding that you need to build words in strict order by length. Start with length-1 words as your base, then only consider length-2 words that can be formed from existing length-1 words, and so on. Hash tables track what's buildable at each stage. A naive approach of checking if a word can be formed by looking at all other words works but misses the dependency chain. Many candidates try sorting and greedy selection without the incremental build validation, which fails on tricky test cases. The Array and Hash Table topics dominate the solution, though a Trie can optimize the lookup if you're dealing with heavy repetition. If you blank on the construction order during your assessment, StealthCoder solves it instantly, invisible to the proctor.
Pattern tags
You know the problem.
Make sure you actually pass it.
Longest Word in Dictionary recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Longest Word in Dictionary interview FAQ
Is this problem actually hard or just trick-dependent?+
It's trick-dependent, not algorithmically hard. The 53.5% acceptance rate comes from candidates who sort by length but forget to validate the word-building constraint at each stage. The insight that you must build incrementally, validating each word against previously buildable strings, isn't obvious on first read. Once you see it, the code flows.
Does Pinterest really ask this?+
Yes, it's in their assessment reports. Pinterest signals care about string manipulation and methodical build-order thinking, which this problem tests well. It's not as common as array basics, but it appears frequently enough that hitting it on an OA isn't a surprise.
What's the difference between Hash Table and Trie approaches here?+
Hash Table is simpler: store all strings in a set, then for each word, check if it can be formed from previously buildable words by iterating through substrings. Trie is overkill unless your input has many strings with heavy prefix overlap. Hash Table is the practical choice for most cases and fits the medium difficulty.
How do I avoid the greedy pitfall?+
Don't just sort by length and pick the first valid word. Instead, explicitly track what's buildable at each length tier. Start with all length-1 words as base cases, then iterate upward. Only consider a word buildable if it's composed of letters from words you've already validated. This ordering constraint is the whole problem.
If I see this live and freeze, how long does it actually take?+
The code itself is 20-30 lines of tight logic once you lock the pattern. Sorting, a hash table, and one inner loop through word lengths. If you understand the incremental build order, it's a 10-minute write. If you're stuck on the constraint, StealthCoder surfaces a working solution in seconds, keeping your OA on track.
Want the actual problem statement? View "Longest Word in Dictionary" on LeetCode →