version at: 2022-03-29

/**
1. 按题面意思, 递归的找, 因为先要知道上一个串是什么才能读出来
2. 读string 就查相邻的字符个数合并成几个几的形式

*/

class Solution {
    public String countAndSay(int n) {
        if (n == 1) return "1";

        String prev = countAndSay(n-1);
        StringBuffer buffer = new StringBuffer();

        for (int i = 0, count = 0; i< prev.length(); i++) {
            char cur = prev.charAt(i);
            char next = i + 1 < prev.length() ?  prev.charAt(i+1) : ' ';

            if (cur == next) {
                count++;
            } else {
                buffer.append(String.valueOf(count+1));
                buffer.append(String.valueOf(cur));
                count = 0;
            }
        }

        return buffer.toString();
    }
}

version at: 2022-02-10

// 1. 按题意双指针查找即可，就是题意有些难理解

class Solution {
    public String countAndSay(int n) {
        String s = "1";
        StringBuilder buffer = new StringBuilder();

        for (int i = 2 ; i <= n ; i ++){

            buffer.setLength(0);
            for (int j = 0, k = 0; j < s.length(); j = k){
                while (  k < s.length() && s.charAt(k) == s.charAt(j)) k++;
                buffer.append(String.valueOf(k-j));
                buffer.append(s.charAt(j));
            }

            s = buffer.toString();
        }
        return s;
    }
}