Kata

Implement the method countIf (count_if in PHP and Python), 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:

function Node(data, next = null) {
  this.data = data;
  this.next = next;
}

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);
  }
}

class Node {
  public $data, $next;
  public function __construct($data, $next = NULL) {
    $this->data = $data;
    $this->next = $next;
  }
}

struct Node {
    struct Node *next;
    int data;
};

class Node:
    def __init__(self, data, next=None): 
        self.data = data
        self.next = next

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

Good luck!

This kata is part of fun with lists series:

• Fun with lists: length
• Fun with lists: indexOf
• Fun with lists: lastIndexOf
• Fun with lists: countIf
• Fun with lists: anyMatch + allMatch
• Fun with lists: filter
• Fun with lists: map
• Fun with lists: reduce