Count and Say
The count-and-say sequence starts with "1" and each subsequent term describes the previous:
- 1: "1"
- 2: "11" (one 1)
- 3: "21" (two 1s)
- 4: "1211" (one 2, one 1)
Given n, return the nth term.
Example:
4
1211
- The sequence starts with "1" as the first term.
- To generate the next term, we describe the previous term: the second term is "11" because the first term has one "1".
- The third term is "21" because the second term has two "1"s.
- The fourth term is "1211" because the third term has one "2" and one "1", which leads to the output for the given input n=4.
Constraints:
- 1 <= n <= 30
Background Knowledge
The count-and-say problem is a classic example of a sequence generation problem, where each term is generated based on the previous term. This type of problem requires an understanding of string manipulation and sequence generation. The key concept here is to analyze the previous term and generate the next term based on a set of rules. In this case, the rule is to describe the previous term by counting the consecutive occurrences of each digit.
To solve this problem, it's essential to have a good understanding of looping constructs and string concatenation. The ability to iterate over a string, count consecutive occurrences of a digit, and append the count and digit to a new string is crucial. Additionally, understanding how to initialize and update variables to keep track of the current term and the next term is important.
The count-and-say sequence is also related to the concept of run-length encoding (RLE), which is a form of data compression where sequences of consecutive identical characters are stored as a single character and a count of the number of times it appears in the sequence. This concept is useful in understanding how to generate each term in the sequence.
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