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Solution: Count and Say

Explore how to generate the count and say sequence by tracking consecutive digits with a single pass approach. Understand how to apply run-length encoding and use the knowing what to track pattern to build each term iteratively. This lesson helps you implement the solution efficiently, analyze time and space complexity, and prepares you for related coding problems in interviews.

Statement

The “count and say” is a sequence of strings built by describing the previous string:

  • The sequence starts with countAndSay(1) = “1”

  • For n > 1, countAndSay(n) is created by run-length encoding the string countAndSay(n - 1).

Run-length encoding (RLE) works by grouping identical consecutive characters and replacing each group with the count of characters followed by the character itself. For example, the string “15224” is read as: one 1, one 5, two 2s, and one 4, producing “11152214”.

Given a positive integer n, return the nthn^{th} string in the count-and-say sequence.

Constraints:

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