Practice/Meta/Leetcode 38. Count and Say

Leetcode 38. Count and Say

CodingOptional

Problem

You are given a positive integer n. Your task is to generate the nth term of a special sequence that follows these rules:

• The first term is "1"
• Each subsequent term is created by reading the previous term aloud, counting consecutive occurrences of each digit

For example:

• Term 1: "1" (given)
• Term 2: Read "1" as "one 1" → "11"
• Term 3: Read "11" as "two 1s" → "21"
• Term 4: Read "21" as "one 2, one 1" → "1211"
• Term 5: Read "1211" as "one 1, one 2, two 1s" → "111221"

The transformation process involves scanning from left to right, grouping consecutive identical digits, and for each group, outputting the count followed by the digit itself.

Requirements

1. Return the nth term of the sequence as a string
2. Start counting from n = 1 (the first term is "1")
3. Process consecutive digit groups correctly
4. Handle the iterative nature of the sequence generation

Constraints

• 1 ≤ n ≤ 30
• Each term will only contain digits from 1 to 3
• The output string will not exceed reasonable length limits for the given constraints

Examples

Example 1:

Input: n = 1 Output: "1" Explanation: The first term is defined as "1".

Example 2:

` Input: n = 4 Output: "1211" Explanation:

• Term 1: "1"
• Term 2: "11" (one 1)
• Term 3: "21" (two 1s)
• Term 4: "1211" (one 2, then one 1) `

Example 3:

` Input: n = 6 Output: "312211" Explanation:

• Term 5: "111221"
• Term 6: "312211" (three 1s, two 2s, one 1) `