Hash - 전화번호 목록

import java.util.Arrays;
import java.util.HashSet;

class Solution {
    public boolean solution(String[] phoneBook) {
        HashSet<String> hashSet = new HashSet<>();
        hashSet.addAll(Arrays.asList(phoneBook));
        
        for (String phoneNum : phoneBook) {
            for (int i=0; i<phoneNum.length(); i++) {
                if (hashSet.contains(phoneNum.substring(0, i))) {
                    return false;
                }
            }
        }
        
        return true;
    }
}