fun-with-lists-countif

Fun with lists: countIf

Implement the method countIf (count_if in PHP), which accepts a linked list (head) and a predicate function, and returns the number of elements which apply to the given predicate.

For example: Given the list: 1 -> 2 -> 3, and the predicate x => x >= 2, countIf / count_if should return 2, since x >= 2 applies to both 2 and 3.

The linked list is defined as follows:

class Node<T> {
  public T data;
  public Node<T> next;
  
  Node(T data, Node next) {
    this.data = data;
    this.next = next;
  }
  
  Node(T data) {
    this(data, null);
  }
}

Note: the list may be null and can hold any type of value.