My humble entry for Dart Dare - Secret Santa. I'm sure there are smaller or faster ways to do this. However, I wanted to try to solve the problem with sorting and processing lists. The entire solution hinges on sorting the santas by last name and by family size. Features of Dart that I used: * Classes * String interpolation * Type annotations * …

secret_santas.dart

class Person {
  String firstName, lastName;
  Person(List<String> raw) : firstName = raw[0], lastName = raw[1];
  String toString() => '$firstName $lastName';
}

/**
 * Expects one person per line, each line containing a first and last name
 * separated by a single space.
 */
List<Person> parsePeople(String santas) {
  return santas
    .split('\n')
    .map((e) => e.trim().split(' '))
    .map((e) => new Person(e))
    .toList();
}

/**
 * Try the old "generate a big sorted list" approach. Sort all people
 * by last name, and then sort again by biggest family down to smallest
 * family. The actual pairing assumes this structure.
 */
List<Person> prepForGiftification(String santas) {
  return ((parsePeople(santas)

    // Group by last name.
    ..sort((p1, p2) => p1.lastName.compareTo(p2.lastName)))

    // Create a list of lists, grouped by last name. Assumes the list is sorted.
    .fold([[]], (List<List> list, person) {
      var current = list.last;
      if (current.isEmpty || current.last.lastName == person.lastName) {
        current.add(person);
      } else {
        list.add([person]);
      }
      return list;
    }) as List

    // Order by biggest family first.
    ..sort((l1, l2) => l2.length.compareTo(l1.length)))

    // Flatten the list of lists.
    .expand((i) => i).toList();
}

/**
 * Assumes a sorted list of people, sorted by biggest family to smallest
 * family.
 *
 * TODO: any error handling at all.
 */
Map<Person, Person> pairUp(List<Person> santas) {
  var pairs = {};
  var currentPairing = santas.indexOf(santas.firstWhere((p) => p.lastName != santas[0].lastName));

  for (var santa in santas) {
    pairs[santa] = santas[currentPairing++];
    if (currentPairing == santas.length) currentPairing = 0;
  }

  return pairs;
}

main() {
  var input = '''
    Zoe Washburne
    Hoban Washburne
    Malcolm Reynolds
    Simon Tam
    River Tam
    Buffy Summers
    Dawn Summers''';

  var people = prepForGiftification(input);
  var pairs = pairUp(people);

  print(pairs);
}

See original Dart Dare description and other solutions: https://plus.google.com/+SethLadd/posts/XjgFRvqtVA4

@sethladd why did you use the : syntax in the Person constructor on line 3, rather than parsing the raw string into first name last name in the constructor body?

@MarkBennett i think it is preparation for optional firstname/lastname lockdown by final keyword. All final fields must be initialized before constructor body begins to run.