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804. Unique Morse Code Words.md

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804. Unique Morse Code Words

leetcode Daily Challenge on November 22th, 2020

Difficulty : Easy

Related Topics : String

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, "cab" 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 "--...--.".

Note:

  • The length of words will be at most 100.
  • Each words[i] will have length in range [1, 12].
  • words[i] will only consist of lowercase letters.

Solution

  • mine
    • Java
      • Runtime: 1 ms, faster than 99.96%, Memory Usage: 36.9 MB, less than 67.82% of Java online submissions 
        // O(N)time
// O(N)space
// N is the all char count
public int uniqueMorseRepresentations(String[] words) {
    if(words == null || words.length == 0) return 0;

    String[] encode = {".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--.."};
    Map<String,Integer> resMap = new HashMap<>();
    for(int i = 0; i < words.length; i++){
        String temp = words[i];
        char[] s = temp.toCharArray();
        StringBuilder sb = new StringBuilder();
        for(int j = 0; j < s.length; j++){
            sb.append(encode[s[j] - 'a']);
        }
        resMap.put(sb.toString(),1);
    }
    return resMap.size();
}
  • the most votes
  • Runtime: 1 ms, faster than 99.96%, Memory Usage: 36.8 MB, less than 67.82% of Java online submissions 
    // O(S)time
// O(S)space
// S is the sum of the lengths of words in words
public int uniqueMorseRepresentations(String[] words) {
    String[] MORSE = new String[]{".-","-...","-.-.","-..",".","..-.","--.",
                     "....","..",".---","-.-",".-..","--","-.",
                     "---",".--.","--.-",".-.","...","-","..-",
                     "...-",".--","-..-","-.--","--.."};

    Set<String> seen = new HashSet();
    for (String word: words) {
        StringBuilder code = new StringBuilder();
        for (char c: word.toCharArray())
            code.append(MORSE[c - 'a']);
        seen.add(code.toString());
    }

    return seen.size();
}