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Talking Through Complexity in a Live Round

In a live coding round the interviewer grades the explanation as well as the code. Several firms are reported to probe it directly: some technical rounds ask for time and space complexity as you go, and others follow a correct answer by asking how a different data structure would change it. A candidate who writes the right code in silence and then says "it's O(nlog⁡n)O(n \log n), I think" gives away marks they had already earned.

This lesson is about what to say, and when.

Name the sizes before the complexity

O(n)O(n) means nothing until nn has a meaning. Most interview problems have more than one size: nn trades, mm distinct symbols, kk results, ww ticks in a window. Say which letter stands for what before the first complexity claim, and keep the letters separate. O(n+mlog⁡k)O(n + m \log k) tells the interviewer that aggregating trades and ranking symbols are different costs. O(nlog⁡n)O(n \log n) for the same solution suggests you have not thought about it.

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