[Programmers] 해시 lv1 - 폰켓몬

https://school.programmers.co.kr/learn/courses/30/lessons/1845?language=javascript 

프로그래머스

function solution(nums) {
    const hash = {};
    
    nums.forEach((n) => {
        if(hash[n] === undefined) hash[n] = 1;
        else hash[n] += 1;
    });
    
    const M = nums.length/2;
    const keyList = Object.keys(hash);

    return M >= keyList.length ? keyList.length : M;
}