38. 外观数列

38. 外观数列

class Solution {
    public String countAndSay(int n) {
        if (n == 1)
            return "1";
        String ans = "1";
        for (int i = 2; i <= n; i++) {
            ans = next(ans);
        }
        return ans;
    }
    private String next(String str) {
        // 对字符串str进行描述
        char[] chs = str.toCharArray();
        StringBuilder descripe = new StringBuilder();
        int index = 0;
        int count;
        char cur;
        while (index < chs.length) {
            count = 0;
            cur = chs[index];
            while (index < chs.length && chs[index] == cur) {
                ++count;
                ++index;
            }
            descripe.append(count);
            descripe.append(cur);
        }
        return descripe.toString();
    }
}