How to solve Leetcode 804. Unique Morse Code Words

Problem statement

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.

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

Constraints

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

Solution: Store the transformations in a set

Code

#include <iostream>
#include <vector>
#include <unordered_set>
using namespace std;
int uniqueMorseRepresentations(vector<string>& words) {
    vector<string> morse{".-", "-...", "-.-.", "-..", ".", "..-.", "--.",
                        "....", "..", ".---", "-.-", ".-..", "--", "-.",
                        "---", ".--.", "--.-", ".-.", "...", "-", "..-",
                        "...-", ".--", "-..-", "-.--", "--.."};
    unordered_set<string> transformations;
    for (string& w : words) {
        string s{""};
        for (char& c : w) {
            s += morse[c - 'a'];
        }
        transformations.insert(s);
    }
    return transformations.size();
}
int main() {
    vector<string> words{"gin","zen","gig","msg"};
    cout << uniqueMorseRepresentations(words) << endl;
    words = {"a"};
    cout << uniqueMorseRepresentations(words) << endl;
}

Output:
2
1

Complexity

Runtime: O(N*M), where N = words.length and M = words[i].length.
Extra space: O(N).

References

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Nhut Nguyen