find_nth_from_tail_in_linked_list.dart

/// Given a pointer to the head of a linked list and a specific position, determine the data value at that position. Count backwards from the tail node. The tail is at postion 0, its parent is at 1 and so on.
/// https://www.hackerrank.com/challenges/get-the-value-of-the-node-at-a-specific-position-from-the-tail
int? findNthElementInList(Node? head, int n) {
  var current = head;
  var counter = 0;
  Node? result = head;
  while (current != null) {
    // when we processed nth element in list let's move result pointer to its next object
    if (counter > n) {
      result = result!.next;
    }
    // keep track of the amount of processed Nodes
    counter++;
    current = current.next;
  }

  return result?.value;
}

void main() {
  var l1 = Node<int>(-3, Node(4, Node(5, Node(6, Node(7, Node(8))))));
  print(("Find nth element from tail in a ll:"));
  print(findNthElementInList(l1, 5)); // -3
  print(findNthElementInList(l1, 0)); // 8
  print(findNthElementInList(l1, 1)); // 7
  print(findNthElementInList(l1, 3)); // 5
  print(findNthElementInList(null, 3)); // null
}

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

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