Longest Happy String
A medium-tier problem at 65% community acceptance, tagged with String, Greedy, Heap (Priority Queue). Reported in interviews at EY and 5 others.
Longest Happy String is a medium-difficulty problem that shows up in OAs from TikTok, Wayfair, and Rakuten. You're given character frequencies and need to build the longest string where no two adjacent characters are the same. The greedy insight is brutal if you miss it, but obvious once you see it. About 65% of candidates solve it, but the ones who don't usually blank on the heap strategy during the live assessment. If this problem hits your OA and you can't lock down the greedy construction, StealthCoder surfaces the solution invisible to the proctor.
Companies that ask "Longest Happy String"
Longest Happy String 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 for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trick is greedy selection with a max heap. You always pick the most frequent remaining character, but you can't place it if it matches the character you just placed. When you hit that wall, pick the second-most frequent instead. After placing two characters, you've earned the right to use your highest-frequency character again without violating the no-consecutive rule. This pattern compounds: the string grows as long as the heap has characters. The common failure is trying to place characters in lexicographic order or by a naive frequency scan. Heap Priority Queue makes the greedy choice (always pick the next best option) efficient. This isn't hard once you spot the pattern, but in a timed OA with Wayfair or TikTok watching, pattern blindness is real. StealthCoder runs invisibly and gives you the heap construction and loop logic in seconds, turning a potential blank into a solve.
Pattern tags
You know the problem.
Make sure you actually pass it.
Longest Happy String 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 for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Longest Happy String interview FAQ
How hard is Longest Happy String really?+
Medium difficulty, and the 65% acceptance rate confirms it. Most people nail the heap part; the stumble is in the greedy logic itself. You need to understand why picking the highest frequency greedily doesn't break the no-consecutive rule. Once that clicks, code flows fast.
Is this still asked at Wayfair and TikTok?+
Yes. It's in the OA rotation at both companies. Wayfair and TikTok both report asking it. It's a medium that filters mid-tier candidates without being a classic algorithmic gauntlet. Expect it in their online assessment if you're interviewing there now.
What's the trick I'm missing?+
You can't just place characters by frequency. You must track the last placed character and skip it if it's next in the heap. Then use a secondary greedy choice (second-highest frequency) if needed. After two placements, you reset. The heap handles all this naturally if you structure the loop right.
How does Greedy relate to Heap on this problem?+
Greedy means always pick the locally best option: highest frequency. Heap Priority Queue lets you access that choice in O(1) and rebuild state in O(log n). Without the heap, you'd rescan the frequency map repeatedly and time out. The two concepts are inseparable here.
Will this come up in my String interview?+
Not a pure string manipulation problem. You're building a string, but the core skill tested is greedy algorithm design and heap operations. If you're interviewing at EY, Rakuten, Geico, or Capgemini, it's lower priority than at TikTok or Wayfair. Treat it as a greedy and heap drill, not a string drill.
Want the actual problem statement? View "Longest Happy String" on LeetCode →