gemstone.dart

/// https://www.hackerrank.com/challenges/gem-stones/problem
///
/// There is a collection of rocks where each rock has various minerals embedded in it. Each type of mineral is designated by a lowercase letter in the range .
/// There may be multiple occurrences of a mineral in a rock. A mineral is called a gemstone if it occurs at least once in each of the rocks in the collection.
///

int calcGemStones(List<String> input) {
  var map = {};
  // go over the input collection and calculate amount of string where the character is present
  // In order not to count "aaa" as three times we maintain ignoreSet set
  for (var string in input) {
    Set ignoreSet = {};
    for (var i = 0; i < string.length; i++) {
      if (ignoreSet.contains(string[i])) {
        continue;
      }
      // init in case value is  new
      map[string[i]] ??= 0;
      map[string[i]] += 1;
      // remember the character and ignore it in next loops
      ignoreSet.add(string[i]);
    }
  }
  var length = input.length;
  // if amount of appearances is equal to amount of input strings
  // then we found a gem and add +1 to counter
  return map.values.fold<int>(0, (previousValue, element) {
    if (element == length) {
      previousValue++;
    }
    return previousValue;
  });
}

void main() {
  var input = ["abc", "bc", "cba"];
  print("Gem stones");
  print(calcGemStones(input)); // 2
  input = ['abcdde', 'baccd', 'eeabg']; // 2
  print(calcGemStones(input));
  input = ['basdfj', 'asdlkjfdjsa', 'bnafvfnsd', 'oafhdlasd']; // 4
  print(calcGemStones(input));
  input = ['a', 'b', 'c', 'd']; // 0
  print(calcGemStones(input));

  input = ['a', 'ab', 'ca', 'dddbbbbbcaccd']; // 1
  print(calcGemStones(input));
}