804. Unique Morse Code Words

1. Description

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:
[".-","-…","-.-.","-..",".","..-.","–.","….","..",".—","-.-",".-..","–","-.","—",".–.","–.-",".-.","…","-","..-","…-",".–","-..-","-.–","–.."]

Given an array of strings words where each word can be written as a concatenation of the Morse code of each letter.

• For example, “cab” can be written as “-.-..–…”, which is the concatenation of “-.-.”, “.-”, and “-…”. We will call such a concatenation the transformation of a word.

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

2. Example

Example 1:
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 “–…–.”.

Example 2:
Input: words = [“a”]
Output: 1

3. Constraints

• 1 <= words.length <= 100
• 1 <= words[i].length <= 12
• words[i] consists of lowercase English letters.

4. Solutions

Hash Table

n is all words' letters count
Time complexity: O(n)
Space complexity: O(n)

class Solution {
public:
    int uniqueMorseRepresentations(vector<string> &words) {
        unordered_set<string> codes;
        for (string word : words) {
            string code;
            for (char letter : word) {
                code.append(code_[get_index_(letter)]);
            }

            codes.insert(move(code));
        }

        return codes.size();
    }

private:
    array<string, 26> code_{".-",   "-...", "-.-.", "-..",  ".",   "..-.", "--.",  "....", "..",
                            ".---", "-.-",  ".-..", "--",   "-.",  "---",  ".--.", "--.-", ".-.",
                            "...",  "-",    "..-",  "...-", ".--", "-..-", "-.--", "--.."};
    inline int get_index_(char letter) {
        return letter - 'a';
    }
};