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Solution: Count and Say

Explore how to solve the count and say sequence by tracking consecutive digits efficiently. Learn to apply the knowing what to track pattern to generate each term using run-length encoding. This lesson helps you develop a clear algorithmic approach for building string sequences and improves your ability to handle similar coding interview problems.

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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