[#98][프로그래머스][입문] 다음에 올 숫자

function solution(common) {
    let answer = 0;
    let len = common.length;
    let diff = common[1] - common[0]; 
    let divide = common[1] / common[0]; 
    if (common[1] - common[0] === common[2] - common[1]) {
        // 등차수열
        return common[len - 1] + diff;
    } else {
        // 등비수열
        // if (common[1] - common[0] !== common[2] - common[1]) {
        return common[len - 1] * divide;
        // return common[len - 1] * divide;
    }
    
}