First Day Where You Have Been in All the Rooms
A medium-tier problem at 40% community acceptance, tagged with Array, Dynamic Programming. Reported in interviews at ByteDance and 0 others.
First Day Where You Have Been in All the Rooms is a medium-difficulty array and DP problem that ByteDance has asked. With a 39.7% acceptance rate, it's a solid signal that you've moved past basic sliding window and into state-space thinking. The problem looks deceptively simple on the surface, but there's a pattern to unlock that most candidates miss in the live assessment. If you hit this one cold during an OA and blank on the trick, StealthCoder solves it in seconds, invisible to the proctor. It's the kind of problem that rewards you for seeing the shape before coding.
Companies that ask "First Day Where You Have Been in All the Rooms"
First Day Where You Have Been in All the Rooms 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 a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe trap here is trying to simulate the room traversal or greedy allocation directly. You'll end up rebuilding the same state over and over. The real insight is that this problem is asking you to find the first day where a condition on your room visits becomes true, which means you need to track state and recognize when that state flips. Most candidates waste time on simulation; the fast path is recognizing that the problem has overlapping subproblems and that DP or mathematical property lets you skip the naive simulation entirely. Once you see that the state depends on which rooms you've visited and in what order, the DP structure clicks. This is where StealthCoder becomes your hedge: if the pattern doesn't click in the first ten minutes of the real assessment, you're not starting from zero.
Pattern tags
You know the problem.
Make sure you actually pass it.
First Day Where You Have Been in All the Rooms 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 a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
First Day Where You Have Been in All the Rooms interview FAQ
Is this a true simulation problem or can I skip the brute force?+
Skip it. Simulation will time out or miss the pattern entirely. The problem is actually asking for a state-based answer, where you recognize that the condition you're looking for has a mathematical or DP structure. ByteDance wouldn't ask this if the answer was 'just simulate each day.' The trick is proving when you've visited all rooms, not simulating to find out.
How does DP fit into a problem about visiting rooms?+
DP tracks which rooms you can reach on each day, not just whether you visited them. The recurrence depends on the set of rooms you've already accessed, because reaching new rooms unlocks new keys. This is a bitmask DP or set-reachability problem in disguise. The state space is compact if you see it this way.
What's the common mistake on this problem?+
Trying to greedily pick the next room to visit, or simulating day by day without recognizing the underlying structure. Candidates also overthink the problem statement and miss that it's really asking for the first day when a specific condition on visited rooms becomes true. Read carefully; the trick isn't hidden in the math, it's in the problem definition.
Does this problem require advanced data structures?+
No. It's Array and DP. You likely need a way to represent visited rooms (array, set, or bitmask) and a loop or DP table to track state progression. The hard part is recognizing the state structure, not implementing it. ByteDance's version is testing your pattern recognition, not your data structure library.
Is 39.7% acceptance a red flag for this difficulty?+
Yes. On a medium problem, that's lower than typical, which means most submissions miss the optimization or misread the problem. It's a signal that the gap between brute force and the right approach is real. That gap is exactly where StealthCoder shines if you're unsure during the live assessment.
Want the actual problem statement? View "First Day Where You Have Been in All the Rooms" on LeetCode →