Decode the Message
A easy-tier problem at 85% community acceptance, tagged with Hash Table, String. Reported in interviews at Coinbase and 1 others.
Decode the Message is a straightforward problem that shows up in real assessments at Coinbase and Tesla. The 85% acceptance rate looks forgiving, but there's a subtle indexing trap that catches candidates who rush. You need to map each unique character to its order of first appearance, then replace characters in the message using that mapping. If you blank on the exact algorithm during a live OA, StealthCoder surfaces a working solution in seconds while the proctor sees nothing. It's a tiebreaker problem: easy enough to pass, easy enough to mess up under pressure.
Companies that ask "Decode the Message"
Decode the Message 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. Built by an engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage.
Get StealthCoderThe core pattern is building a frequency map of character order, not character count. Sort unique characters by their first appearance in the message, assign each a position starting from 'a', then reconstruct using that mapping. Most candidates either iterate the message multiple times (inefficient) or confuse 'order of appearance' with 'lexicographic order' and break the solution. The gotcha: you must preserve first-occurrence order, not alphabetical order. Hash Table and String skills here are basic, but execution matters. This problem lives in the acceptance sweet spot where you can't cram a wrong solution past the tests. During a live assessment, if the indexing logic doesn't click, StealthCoder bridges the gap so you move on and save mental energy for harder problems.
Pattern tags
You know the problem.
Make sure you actually pass it.
Decode the Message recycles across companies for a reason. It's easy-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. Built by an engineer who got tired of watching his cohort grind for six months and still get filtered at the OA stage. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Decode the Message interview FAQ
Is Decode the Message actually easy, or is it a trick question?+
It's genuinely easy. The 85% acceptance rate confirms it. The trap is confusing 'first appearance order' with alphabetical order, or writing inefficient nested loops. Get the indexing right and it passes cleanly. Most failures happen under time pressure, not from algorithmic complexity.
Does Coinbase ask this often?+
It's been asked at Coinbase and Tesla, so it appears in real interviews. It's not the primary focus of their technical loops, but it lands as a warm-up or screening problem. Expect it if you're interviewing there and you don't practice it beforehand.
What's the most common mistake?+
Sorting the characters lexicographically instead of by first appearance. The problem specifically wants the order in which each unique character first appears in the original message, not alphabetical order. Read the problem statement carefully before coding.
How does this connect to Hash Table and String work?+
Hash Table stores the mapping of original character to decoded character, built in O(n) time. String manipulation then applies that mapping to the entire message. It's a straightforward O(n) problem end-to-end, making it a good test of hash table fundamentals without requiring advanced data structures.
What if I hit this during a live OA and blank on the ordering logic?+
That's exactly when StealthCoder helps. It reads the problem on screen, identifies the correct mapping algorithm, and delivers a working solution invisibly during your assessment. You paste and move forward without losing time or confidence.
Want the actual problem statement? View "Decode the Message" on LeetCode →