720. Longest Word in Dictionary

class Solution {
    public String longestWord(String[] words) {
        Set<String> wordSet = new HashSet<>(Arrays.asList(words));
        Arrays.sort(words, (o1, o2) -> {
            int diff = Integer.compare(o2.length(), o1.length());
            if (diff != 0) {
                return diff;
            } else {
                return o1.compareTo(o2);
            }
        });

        for (String word : words) {
            if (match(word, wordSet)) {
                return word;
            }
        }
        return "";
    }

    private boolean match(String word, Set<String> wordSet) {
        for (int endIndex = word.length() - 1; endIndex > 0; endIndex--) {
            if (!wordSet.contains(word.substring(0, endIndex))) {
                return false;
            }
        }

        return true;
    }
}

References

720. Longest Word in Dictionary