프로그래머스 - 다음에 올 숫자

class Solution {
    public int solution(int[] common) {
        int answer = 0;
        if(common[1] - common[0] == common[2] - common[1]){
            answer = common[common.length-1] + common[1] - common[0];
        }
        else{
            answer = common[common.length-1] * (common[1] / common[0]);
        }
        return answer;
    }
}