​LeetCode刷题实战481：神奇字符串

示例 1：
输入：n = 6
输出：3
解释：神奇字符串 s 的前 6 个元素是 “122112”，它包含三个 1，因此返回 3 。

示例 2：
输入：n = 1
输出：1

class Solution {
    public int magicalString(int n) {
        if(n <= 0)
            return 0;
        if(n <= 3)
            return 1;
        StringBuilder base = new StringBuilder();
        StringBuilder sub = new StringBuilder();
        base.append("122");
        sub.append("12");
        int index = 0;
        int temp = 0;
        int counts = 1;
        while (base.length() < n){
            index = sub.length();
            temp = base.charAt(index)-'0';
            sub.append(temp);
            if(temp==2){
                temp = base.charAt(base.length()-1)-'0';
                if(temp == 2){
                    base.append("11");
                    if(base.length() <= n)
                        counts += 2;
                    else
                        counts += 1;
                }else {
                    base.append("22");
                }
            }else {//temp == 1
                temp = base.charAt(base.length()-1)-'0';
                if(temp == 2){
                    base.append("1");
                    counts += 1;
                }else {
                    base.append("2");
                }
            }
        }
        return counts;
    }
}