Class Solution


  • public class Solution
    extends Object
    38 - Count and Say.

    Medium

    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 the nth 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
    • Constructor Detail

      • Solution

        public Solution()
    • Method Detail

      • countAndSay

        public String countAndSay​(int n)