java 题解LeetCode38外观数列示例

class Solution {
    public String countAndSay(int n) {
        String num = "1";
        String result = "1";
        char a = 'a';
        int flag = 0;
        for(int i = 1;i<n;i++) {
            result = "";
            a = 'a';
            flag = 0;
            while(true) {
                if(num.length() == 0) {
                    result = result + flag + a;
                    num = result;
                    break;
                }
                char c = num.charAt(0);
                if(a == c) {
                    flag++;
                }else {
                    if(a != 'a') {
                        result = result + flag + a;
                    }
                    a = c;
                    flag = 1;
                }
                num = num.substring(1);
            }
        }
        return result;
    }
}

class Solution {
    public String countAndSay(int n) {
        if(n == 1) {
            return "1";
        }
        StringBuilder result = new StringBuilder();
        String s = countAndSay(n-1);
        int len = s.length();
        int a = 0;
        for(int i = 1;i<len +1;i++) {
            if(i == len) {
                return result.append(i-a).append(s.charAt(a)).toString();
            }else if (s.charAt(i)!=s.charAt(a)) {
                result.append(i-a).append(s.charAt(a));
                a = i;
            }
        }
        return result.toString();
    }
}