804. Unique Morse Code Words

International Morse Code defines a standard encoding where each letter is mapped to a series of dots and dashes, as follows: "a" maps to ".-", "b" maps to "-...", "c" maps to "-.-.", and so on.

For convenience, the full table for the 26 letters of the English alphabet is given below:

[".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--.."]

Now, given a list of words, each word can be written as a concatenation of the Morse code of each letter. For example, "cba" can be written as "-.-..--...", (which is the concatenation "-.-." + "-..." + ".-"). We'll call such a concatenation, the transformation of a word.

Return the number of different transformations among all words we have.

Example:
Input: words = ["gin", "zen", "gig", "msg"]
Output: 2
Explanation: 
The transformation of each word is:
"gin" -> "--...-."
"zen" -> "--...-."
"gig" -> "--...--."
"msg" -> "--...--."

There are 2 different transformations, "--...-." and "--...--.".

解题要点：

遍历整个数组，用HashSet存数组里元素对应的摩斯电码，返回这个HashSet的长度。（存入HashSet的字符串具有唯一性）

class Solution {
    public int uniqueMorseRepresentations(String[] words) {
        String[] morse = {".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--.."};

        Set<String> set = new HashSet();
        for(String word : words){
            StringBuilder sb = new StringBuilder();
            for(int i = 0; i < word.length(); i++){
                char cc = word.charAt(i);
                String temp = morse[cc - 'a'];
                sb.append(temp);
            }
            set.add(sb.toString());
        }
        
        return set.size();
    }
}