最常使用的K个单词II · Top K Frequent Wor

import java.util.NavigableSet;

public class TopK {
private Map<String, Integer> words = null;
private NavigableSet<String> topk = null;
private int k;

private Comparator<String> myComparator = new Comparator<String>() {
    public int compare(String left, String right) {
        if (left.equals(right))
            return 0;

        int left_count = words.get(left);
        int right_count = words.get(right);
        if (left_count != right_count) {
            return right_count - left_count;
        }
        return left.compareTo(right);
    }
};

public TopK(int k) {
    // initialize your data structure here
    this.k = k;
    words = new HashMap<String, Integer>();
    topk = new TreeSet<String>(myComparator);
}

public void add(String word) {
    // Write your code here
    if (words.containsKey(word)) {
        if (topk.contains(word))
            topk.remove(word);
        words.put(word, words.get(word) + 1);
    } else {
        words.put(word, 1);
    }

    topk.add(word);
    if (topk.size() > k) {
        topk.pollLast();
    }
}

public List<String> topk() {
    // Write your code here
    List<String> results = new ArrayList<String>();
    Iterator it = topk.iterator();
    while(it.hasNext()) {
         String str = (String)it.next();
         results.add(str);
    }
    return results;
}

}