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MediumPrep Room Coding #1915

String concatenation quadratic allocation

Code reviewAlgorithms & data structuresMid–Senior~18 min

Review this Java method that renders a CSV body from rows. It works for small exports but a customer report with ~200k rows takes minutes and spikes GC.

What a strong answer looks like

Separate real bugs from style. Rank issues by severity, point at the root cause rather than the symptom, and suggest a concrete fix, specific and kind.

0:00 of about 18 min
Mark a line and say what kind of problem it is.0 findings
1String toCsv(List<Row> rows) {
2 String out = "";
3 for (Row r : rows) {
4 out = out + r.id() + "," + r.name() + "," + r.amount() + "\n";
5 }
6 return out;
7}
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.