My first instinct was to just load it and scan, which is obviously wrong given the constraint.
Start by clarifying the constraints: is the string stored on disk, streamed, or distributed? Then propose a streaming solution that reads the string in chunks, counts spaces, and handles chunk boundaries by carrying over the last character. For scalability, discuss parallelizing across multiple machines with careful boundary handling.
Pro tip: Mention that you can avoid double-counting spaces at chunk boundaries by tracking whether the previous chunk ended with a space and the current chunk starts with a space, and only count a space if it's not part of a run that was already counted.
Ask about the source of the string (file, stream, distributed storage), whether it's static or dynamic, and if there are memory or time constraints. Confirm that 'split on spaces' means counting spaces as delimiters, not necessarily storing the split parts.
Read the string in fixed-size chunks (e.g., 1MB) sequentially, maintaining a running count of spaces. Handle chunk boundaries by checking if the last character of the previous chunk and the first character of the current chunk are both spaces to avoid double-counting.
If the string is on distributed storage (e.g., HDFS), split it into blocks, process each block in parallel, and then combine results. Ensure boundary spaces are counted correctly by having each mapper emit the first and last character or by using a custom input format.
Compare streaming vs. parallel approaches: streaming is simple but single-threaded; parallel is faster but requires coordination. Mention optimizations like using memory-mapped files, SIMD instructions, or regex for faster scanning.
Reiterate the chosen approach based on constraints, emphasizing correctness and efficiency. Mention that the solution can be adapted to count words or split the string if needed.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.