38. Count and Say

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, generate the nth 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"

Solution

public class Solution {
    public String countAndSay(int n) {

                  StringBuilder s1 = new StringBuilder("1");
        StringBuilder s2 = new StringBuilder();
        for (int i = 2; i <= n; i++) {


            int m = 0;
            while (m < s1.length()) {

                int p = m + 1;
                while (p < s1.length() && s1.charAt(m) == s1.charAt(p)) {
                    p ++;
                }

                s2.append((p -m) +"");
                s2.append(s1.charAt(m));

                m = p;


            }

            s1 = s2;
            s2 = new StringBuilder();
        }

        return s1.toString();}
}