[level 2] 전화번호 목록 - 42577

문제 링크

class Solution {

    public boolean solution(String[] phone_book) {
       HashMap<String, Boolean> map = new HashMap<>();
       for (String number : phone_book) {
          map.put(number, true);
       }

       for (String number : phone_book) {
          for (int i = 1; i < number.length(); i++) {
             if (map.containsKey(number.substring(0, i))) {
                return false;
             }
          }
       }
       return true;
    }
}