369 게임

class Solution {
    public int solution(int order) {
        int answer = 0;
        String str = Integer.toString(order);
        int count=0;
        for(int i=0; i<str.length(); i++){
            char ch = str.charAt(i); // 
            if(ch=='3' || ch=='6' || ch=='9') {
                count++;
            }
        }
        return count;
    }
}