⭐️ 코드 (HashSet 이용) import java.util.*; class Solution { public boolean solution(String[] phone_book) { boolean answer = true; HashSet hashSet = new HashSet(); for (int i = 0; i < phone_book.length; i++) { hashSet.add(phone_book[i]); } for (int i = 0; i < phone_book.length; i++) { for (int j = 0; j < phone_book[i].length(); j++) { if (hashSet.contains(phone_book[i].substring(0, j))) { return fals..