Array challenge

challenge.dart

// Have the function ArrayChallenge(strArr)
// read the array of strings stored in strArr, which will contain 2 elements:
// the first element will be a sequence of characters,
// and the second element will be a long string of comma-separated words, in alphabetical order,
// that represents a dictionary of some arbitrary length.
// For example: strArr can be: ["hellocat", "apple,bat,cat,goodbye,hello,yellow,why"].
// Your goal is to determine if the first element in the input can be split into two words,
// where both words exist in the dictionary that is provided in the second input.
// In this example, the first element can be split into two words:
// hello and cat because both of those words are in the dictionary.
// Your program should return the two words that exist in the dictionary separated by a comma.
// So for the example above, your program should return hello,cat.
// There will only be one correct way to split the first element of characters into two words.
// If there is no way to split string into two words that exist in the dictionary, return the string not possible.
// The first element itself will never exist in the dictionary as a real word.
// Once your function is working, take the final output string and concatenate it with your ChallengeToken,
// and then replace every third character with an X.

// Your ChallengeToken: pq7kbawue985

// Examples

// Input: ["baseball", "a,all,b,ball,bas,base,cat,code,d,e,quit,z"]
// Output: base,ball
// Final Output: baXe,XalXpqXkbXwuX98X

// Input: ["abcgefd", "a,ab,abc,abcg,b,c,dog,e,efd,zzzz"]
// Output: abcg,efd
// Final Output: abXg,XfdXq7XbaXueX85

String arrayChallenge(List<String> strArr) {
  String word = strArr[0];
  List<String> dictionary = strArr[1].split(",");

  final dictionarySet = dictionary.toSet();
  final prefixes = <String>{};

  for (int i = 1; i < word.length; ++i) {
    String prefix = word.substring(0, i);

    if (dictionarySet.contains(prefix)) {
      prefixes.add(prefix);
    }
  }

  for (String prefix in prefixes) {
    String suffix = word.substring(prefix.length);

    if (dictionarySet.contains(suffix)) {
      return '$prefix,$suffix';
    }
  }

  return "not possible";
}

String generateFinalOutput(String output, String token) {
  String combinedValue = output + token;

  List<String> characters = combinedValue.split('');

  for (int i = 2; i < characters.length; i += 3) {
    characters[i] = 'X';
  }
  return characters.join('');
}

void main() {
  String challengeToken = "pq7kbawue985";
  print(generateFinalOutput(
      arrayChallenge(["baseball", "a,all,b,ball,bas,base,cat,code,d,e,quit,z"]),
      challengeToken));
  print(generateFinalOutput(
      arrayChallenge(["abcgefd", "a,ab,abc,abcg,b,c,dog,e,efd,zzzz"]),
      challengeToken));
}