https://programmers.co.kr/learn/courses/30/lessons/12915?language=javascript
function solution(strings, n) {
var answer = [];
const hashMap = {};
const sortBy = [];
for(let i = 0; i < strings.length; i++) {
console.log(strings[i])
sortBy.push(`${strings[i][n]} + ${strings[i]}`);
hashMap[`${strings[i][n]} + ${strings[i]}`] = strings[i];
}
sortBy.sort();
for(let i = 0; i < sortBy.length; i++) {
answer.push(hashMap[sortBy[i]]);
}
return answer;
}