PPractick

The problem

You're building a toy "data compression" utility for an embedded systems team — the simplest possible run-length encoding demo used in onboarding material for new hires. The classic illustrative example is the count-and-say sequence: each term is generated by "reading off" the previous term, describing consecutive runs of the same digit as (count)(digit). Your task: given n, generate the n-th term of this sequence.

The sequence starts:1 11 (one 1) 21 (two 1s) 1211 (one 2, one 1) 111221 (one 1, one 2, two 1s) 312211 (three 1s, two 2s, one 1)

Function signature

string countAndSay(int n);

Test cases

Input n	Output	Explanation
1	"1"	Base case
2	"11"	"one 1" → "11"
3	"21"	"two 1s" → "21"
4	"1211"	"one 2, one 1" → "1211"
5	"111221"	"one 1, one 2, two 1s" → "111221"
6	"312211"	"three 1s, two 2s, one 1" → "312211"
7	"13112221"	One more iteration applied to "312211"

How interviewers phrase it

• "Generate the n-th term of the count-and-say sequence."
• "Given a starting string '1', repeatedly apply run-length-encoding-style description n-1 times — what's the result?"
• This is LeetCode 38 — generally considered an easier/medium problem despite the "Hard" tag here; interviewers often use it as a warm-up simulation problem before moving to something harder, or to test clean string-building habits.

Clarifying questions to ask

1. Is n 1-indexed (i.e., n=1 returns "1")? (Standard convention — confirm.)
2. What's the expected range of n? (LeetCode constraints: 1 <= n <= 30 — small range, since the string length grows roughly exponentially with n, so don't worry about extreme optimization here, but mention the growth rate awareness.)
3. Should digits be assumed single-digit only, or could counts exceed 9 (e.g., ten consecutive same digits) requiring multi-digit counts? (For n <= 30, this won't happen in practice, but worth flagging as an edge case to be aware of.)
4. Any specific output format expectations (string vs vector of digits)?

Follow-ups to expect

1. "What's the time/space complexity, and how does the string length grow with n?"
2. "Can you do this without using extra string concatenation overhead (e.g., StringBuilder-style efficient builds)?"
3. "What if counts could exceed 9 (multi-digit run lengths)? How would your code change?"
4. "Can you do this iteratively without recursion, and what are the tradeoffs?"
5. "Is there a closed-form or pattern-based shortcut to skip directly to term n without generating all previous terms?"

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