Count And Say

Count And Say string

The count-and-say sequence is the sequence of integers beginning as follows: 1, 11, 21, 1211, 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, generate the nth sequence.

Note: The sequence of integers will be represented as a string.

Count And Say Solution

public class CountAndSay {
    public String countAndSay(int n) {
        String s = "1";

        for(int i = 1; i < n; i++) {
            s = helper(s);
        }

        return s;
    }

    public String helper(String s) {
        StringBuilder sb = new StringBuilder();
        char c = s.charAt(0);
        int count = 1;

        for(int i = 1; i < s.length(); i++) {
            if(s.charAt(i) == c) {
                count++;
            } else {
                sb.append(count);
                sb.append(c);
                c = s.charAt(i);
                count = 1;
            }
        }

        sb.append(count);
        sb.append(c);

        return sb.toString();
    }
}

Last modified October 4, 2020