CareerCup

Parse the file using Files,Paths utility of nio.file package.It would give you a list of string , put that to set to find the duplicate.
List<String> lines = Files.readAllLines(Paths.get(Path), StandardCharsets.UTF_8);

public static Set<String> findDuplicates(List<String> lines) {
 
        final Set<String> setToReturn = new HashSet<String>();
        final Set<String> set1 = new HashSet<String>();
 
        for (String yourInt : listContainingDuplicates) {
            if (!set1.add(yourInt)) {
                setToReturn.add(yourInt);
            }
        }
        return setToReturn;
    }

Saroj Interviewer will kick you out if you give him this program. Checking duplicate strings using hashset. This is not an answer he was expecting.