README.md

38. Count and Say

The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     1
2.     11
3.     21
4.     1211
5.     111221

1 is read off as "one 1" or 11.

11 is read off as "two 1s" or 21.

21 is read off as "one 2, then one 1" or 1211.

Given an integer n where 1 ≤ n ≤ 30, generate the n^th term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

Solutions (Python)

1. Two Pointers

class Solution:
    def countAndSay(self, n: int) -> str:
        s = "1"
        for i in range(n - 1):
            tmp = ""
            i = 0
            for j in range(len(s)):
                if s[i] != s[j]:
                    tmp += str(j - i) + s[i]
                    i = j
            tmp += str(len(s) - i) + s[i]
            s = tmp
        return s

Solutions (Ruby)

1. Two Pointers

# @param {Integer} n
# @return {String}
def count_and_say(n)
    s = "1"

    for _ in 1...n
        tmp = ""
        i = 0

        for j in 0...s.length
            if s[i] != s[j]
                tmp += (j - i).to_s + s[i]
                i = j
            end
        end

        tmp += (s.length - i).to_s + s[i]
        s = tmp
    end

    return s
end