완주하지 못한 선수

function solution(participants, completions) {
    const map = new Map();

    for(const participant of participants) {
      map.set(participant, (map.get(participant) || 0) + 1);
    }

    for(const completion of completions) {
      map.set(completion, map.get(completion) - 1);
    }

    for(const [key, value] of map.entries()){
      if(value === 1) return key;
    }
}

폰켓몬

function solution(nums) {
    const map = new Map();

    for(const num of nums) {
      map.set(num, (map.get(num) || 0) + 1);
    }

    return map.size >= nums.length / 2 ? nums.length / 2 : map.size;
}

위장

function solution(clothes) {
    const map = new Map();
    let answer = 1;
    
    clothes.forEach(v => {
        map.set(v[1], (map.get(v[1]) || 0) + 1);
    })
    
    for(const value of map.values()){
        answer *= (value + 1);
    }
    
    return answer - 1;
}

베스트앨범

function solution(genres, plays) {
    const answer = [];
    const map = new Map();
    
    genres.forEach((genre, index) => {
        map.set(genre, (map.get(genre) || 0) + plays[index]);
    })
    
    const list = [...map.entries()].sort((a, b) => b[1] - a[1]);
    
    list.forEach((value, index) => {
        const play = plays.map((v, i) => [v, i])
                          .filter((v, i) => genres[i] === value[0])
                          .sort((a, b) => b[0] - a[0])
                          .slice(0, 2);
        
        answer.push(...play.map(v => v[1]));
    })
    
    return answer;
}