private void set(Map<String, Integer> actual, String[] words) {
        for (String word : words) {
            if (actual.containsKey(word)) {
                actual.put(word,  actual.get(word) + 1);
            } else {
                actual.put(word, 1);
            }
        }
    }
References
https://leetcode.com/problems/substring-with-concatenation-of-all-words/
src/com/interview/string/SubtringWithConcatentationOfWords.java