merge_two_ll.dart

class Node<T> {
  T value;
  Node<T>? next;

  Node(this.value, [this.next]);
}

/// Given pointers to the heads of two sorted linked lists, merge them into a single, sorted linked list. Either head pointer may be null meaning that the corresponding list is empty.
/// https://www.hackerrank.com/challenges/merge-two-sorted-linked-lists/
Node? mergeTwoLists(Node? l1, Node? l2) {
  if (l1 == null && l2 == null) {
    return null;
  }

  List data = [];
  // extract all data from linked list nodes into arrays
  while (l1 != null) {
    data.add(l1.value);
    l1 = l1.next;
  }
  while (l2 != null) {
    data.add(l2.value);
    l2 = l2.next;
  }
  data.sort();

  Node? tmp;
  Node? current;
  // convert sorted array into Linked List
  // this will be our final result
  for (var val in data) {
    // handle first case when new LinkedList was not yet created
    if (tmp == null) {
      tmp = Node(val);
      current = tmp;
      continue;
    }
    current!.next = Node(val);
    current = current.next!;
  }

  return tmp;
}

void main() {
  var f1 = Node<int>(1, Node(7, Node(10)));
  var f2 = Node<int>(-3, Node(4, Node(5)));

  print("Merging two lists");
  var result = mergeTwoLists(f1, f2);
  print(result!.value);
  print(result!.next!.value);
  print(result!.next!.next!.value);
}