[NodeJS] 프로그래머스 완주하지 못한 선수

/**
 * @link https://school.programmers.co.kr/learn/courses/30/lessons/42576?language=javascript
 * @description
 */
const solution = (participant, completion) => {
	const map = {};

	for (const p of participant) {
		map[p] = map[p] ? map[p] + 1 : 1;
	}

	for (const c of completion) {
		map[c]--;
	}

	for (const k in map) {
		if (map[k] > 0) {
			return k;
		}
	}
};