[Programmers] 해시 lv2 - 위장

https://school.programmers.co.kr/learn/courses/30/lessons/42578?language=javascript 

프로그래머스

function factorial(n) {
    if(n === 0) return 1;
    let result = 1;
    for(let i = 1 ; i <= n ; i++) {
        result *= i;
    }
    
    return result;
}

function perm(n,m) {
    let n_ = factorial(n);
    let m_ = factorial(m);
    let n_m = factorial(n-m);
    
    return n_/(m_*n_m);
}

function solution(clothes) {
    var answer = 1;
    let typeNumber = 0;
    const hash = {};
    
    clothes.forEach((c) => {
        if(hash[c[1]] === undefined) {
            hash[c[1]] = 1; 
            typeNumber++;
        }
        else hash[c[1]] += 1;
    });
    
    // 종류 1가지
    if(typeNumber === 1) return clothes.length;
    
    const keys = Object.keys(hash);

    keys.forEach((k) => {
       answer *= (perm(hash[k], 1) + perm(hash[k], 0));
    });
    
    return answer -1;
}