Read N Characters Given Read4
A easy-tier problem at 42% community acceptance, tagged with Array, Simulation, Interactive. Reported in interviews at Google and 0 others.
Read N Characters Given Read4 is a 42% acceptance problem despite its EASY tag, which tells you it's a deceptive one. Google asks it. The trick isn't the algorithm, it's the edge case handling. You get a read4() API that returns a chunk of up to 4 characters at a time, and you need to build a wrapper that reads exactly N characters from an unknown-length stream. Most candidates nail the happy path, then fail on boundary conditions: partial reads, exhausted streams, leftover buffer state. If this hits your live assessment and you blank on the read4 contract, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Read N Characters Given Read4"
Read N Characters Given Read4 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 Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code.
Get StealthCoderThe core pattern is simulate a buffered I/O system. You call read4() in a loop, collect bytes, and stop when you've returned N characters or the stream ends. The gotcha: read4() might return fewer than 4 bytes (partial read), which signals EOF, but you still have to respect N. Many solutions ignore the multi-call scenario, if read() is called again on the same stream, your first call's leftover buffer state needs to persist. You need a stateful class with instance variables tracking what read4() returned last and where your buffer pointer sits. The obvious approach (just loop and return) breaks when read() is called multiple times sequentially. That's where the problem shifts from basic to real. StealthCoder's the hedge if you didn't practice the state machine aspect during prep.
Pattern tags
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Read N Characters Given Read4 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 Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Read N Characters Given Read4 interview FAQ
Why is a 42% acceptance rate so high for an EASY problem?+
The read4 pattern isn't taught in standard DSA curriculums. Candidates walk in thinking it's a basic loop, then hit the multi-call state management and panic. It's easy once you see it, hard if you don't.
Do I need to worry about concurrency or thread safety?+
Not indicated in Google's reports of this problem. It's single-threaded simulation. Focus on correctness of state tracking across repeated calls, not locking mechanisms.
What's the most common failure mode?+
Forgetting that read() can be called multiple times on the same stream object. Your first solution works for one call, then subsequent calls return wrong results because you didn't cache unused bytes from the last read4() batch.
How does this relate to Array and Simulation topics?+
You're simulating a file I/O system using an array buffer. The Array aspect is managing your 4-byte cache and pointer logic. It's not hard algorithmically, it's precision engineering of state.
Is there a trick to avoid re-implementing this wrong under pressure?+
Template the state upfront: instance variables for buffered bytes, buffer index, and end-of-file flag. Write your read() as a small dispatcher. If you have the skeleton, the test cases will guide you to correctness.
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