第一题：
大佬看一下哪里错了
public static int dfs(String s, int current) {
        if (current == s.length()) {
            return 0;
        }
        int max = 0;
        for (int i = current; i < s.length(); i++) {
            int a = Integer.parseInt(s.substring(current, i + 1));
            if (a % 3 == 0) {
                max = Math.max(max, dfs(s, i + 1) + 1);
            } else {
                max = Math.max(max, dfs(s, i + 1));
            }
        }
        return max;
    }