class Solution {
    public int solution(String number) {
        int answer = 0;
        return answer;
    }
}

해결법

방법 1

class Solution {
    public int solution(String number) {
        int answer = 0;
        
        String[] str = number.split("");
        
        int sum = 0;
        
        for (int i = 0; i < str.length; i++) {
            sum += Integer.parseInt(str[i]);
            int num = sum % 9;
            sum = num;
        }
        
        answer = sum;
        
        return answer;
    }
}

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