https://programmers.co.kr/learn/courses/30/lessons/12915
func solution(_ strings:[String], _ n:Int) -> [String] {
let answer = strings.sorted { lhs, rhs in
if Array(lhs)[n] == Array(rhs)[n] {
return lhs < rhs
} else {
return Array(lhs)[n] < Array(rhs)[n]
}
}
return answer
}