原题链接: https://oj.leetcode.com/problems/count-and-say/

public String countAndSay(int n) {
    if (n < 0) return "";

    StringBuilder sb = new StringBuilder();

    if (n == 1) {
        return sb.append("1").toString();
    }

    String prevStr = countAndSay(n - 1);
    int length = prevStr.length();
    char prevChar = ' '; 
    int accumulator = 0;

    for (int i = 0; i < length; i++) {
        char c = prevStr.charAt(i);

        if (c == prevChar) {
            accumulator++;
        } else {
            if (prevChar == ' ') {
                prevChar = c;
                accumulator = 1;
                continue;
            }

            sb.append("" + accumulator + prevChar);

            prevChar = c;
            accumulator = 1;
        }
    }

    if (accumulator > 0) sb.append("" + accumulator + prevChar);

    return sb.toString();
}