17. TreeMap and TreeSet

TreeSet

TreeSet<Integer> schedule = new TreeSet<Integer>();
schedule.add(1223);
schedule.add(1430);
schedule.add(1545);
schedule.add(1610);
schedule.add(1705);
schedule.add(2010);
schedule.add(2215);
schedule.add(2320);
schedule.add(2345);

// show the last bus that leaves PGH before 4pm (strictly less than)
System.out.println(schedule.headSet(1600).last());

// show the first bus that leaves PGH after 10pm (greater than or equal to)
System.out.println(schedule.tailSet(2200).first());

TreeMap

Map<String, Integer> freqOfWords = new HashMap<String, Integer>();
String[] words = "coming together is a beginning keeping together is progress working together is success"
        .split(" ");

for (String word : words) {
    Integer frequency = freqOfWords.get(word);
    if (frequency == null) {
        frequency = 1;
    } else {
        frequency++;
    }
    freqOfWords.put(word, frequency);
}

// no specific order in HashMap
System.out.println("Elements in HashMap: " + freqOfWords);

// print freqOfWords in ascending order
TreeMap<String, Integer> sortedWords = new TreeMap<String, Integer>(freqOfWords);

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