Thinking process

• quick look up
• use hash set or hash map

Mistakes

• corner cases!!!
• [], isUnique("a")? => true
• ["a"], isUnique("")? => true
• [""], isUnique("a")? => true

• ["hello"], isUnique("hello")? => true

  • because of this one, I should use hash map

public class ValidWordAbbr {
    private Map<String, String> abbr;

    public ValidWordAbbr(String[] dictionary) {
        abbr = new HashMap<String, String>();

        for (String word : dictionary) {
            String s = getAbbr(word);

            if (abbr.containsKey(s) && !abbr.get(s).equals(word)) {
                abbr.put(s, "");
            } else {
                abbr.put(s, word);
            }
        }
    }

    public boolean isUnique(String word) {
        if (abbr.isEmpty()) return true;
        if (word.length() == 0) return true;

        String s = getAbbr(word);
        return !abbr.containsKey(s) || (abbr.containsKey(s) && abbr.get(s).equals(word));
    }

    private String getAbbr(String str) {
        int len = str.length();
        if (len <= 2) {
            return str;
        } 

        StringBuilder res = new StringBuilder();
        res.append(str.charAt(0));
        res.append(len - 2);
        res.append(str.charAt(len - 1));

        return res.toString();
    }
}


// Your ValidWordAbbr object will be instantiated and called as such:
// ValidWordAbbr vwa = new ValidWordAbbr(dictionary);
// vwa.isUnique("Word");
// vwa.isUnique("anotherWord");