38. Count and Say

The count-and-say sequence is a sequence of digit strings defined by the recursive formula:

• countAndSay(1) = "1"
• countAndSay(n) is the way you would "say" the digit string from countAndSay(n-1), which is then converted into a different digit string.

To determine how you "say" a digit string, split it into the minimal number of groups so that each group is a contiguous section all of the same character. Then for each group, say the number of characters, then say the character. To convert the saying into a digit string, replace the counts with a number and concatenate every saying.

For example, the saying and conversion for digit string "3322251":

Given a positive integer n, return thenth term of the count-and-say sequence.

Example 1:

Input: n = 1
Output: "1"
Explanation: This is the base case.

Example 2:

Input: n = 4
Output: "1211"
Explanation:
countAndSay(1) = "1"
countAndSay(2) = say "1" = one 1 = "11"
countAndSay(3) = say "11" = two 1's = "21"
countAndSay(4) = say "21" = one 2 + one 1 = "12" + "11" = "1211"

Constraints:

• 1 <= n <= 30

# @lc code=start
using LeetCode

function countandsay(n::Int)

Base case

    n == 1 && return "1"

Get the previous term

    previous_term = countandsay(n - 1)

Generate the current term by "saying" the previous term

    current_term = ""
    count = 0
    current_char = previous_term[1]

    for char in previous_term
        if char == current_char
            count += 1
        else
            current_term *= string(count) * current_char
            current_char = char
            count = 1
        end
    end

Append the last group

    current_term * string(count) * current_char
end
# @lc code=end

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