LinkedListUtils

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Nodes
{
    class LinkedListUtils
    {
        public static Node<T> createList<T>(T[] valuesArray)
        {
            Node<T> current = null;

            for (int i = valuesArray.Length - 1; i >= 0; i--)
            {
                if (current != null)
                    current = new Node<T>(valuesArray[i], current);
                else
                    current = new Node<T>(valuesArray[i]);
            }

            return current;
        }


        public static Node<T> leaveOnly<T>(Node<T> pos, Predicate<Node<T>> condition)
        {

            Node<T> first = null,
                        lastValid = null;

            while (pos != null)
            {
                if (condition(pos)) // if the elements meets the condition
                {
                    if (first == null) // if first element was not set yet, set it to the one found now
                        first = pos;
                    else // if a first element was set already, add pointer to last element
                        lastValid.setNext(pos);

                    lastValid = pos;
                }

                pos = pos.getNext(); // move to next element
            }

            return first;
        }

        public static Node<T> remove<T>(Node<T> pos, Predicate<Node<T>> condition)
        {
            return leaveOnly<T>(pos,
                node => !condition(node) // lambda expression for making a 'not' predicate
              );
        }

        public static string toString<T>(Node<T> pos)
        {
            string list = "[";

            while (pos != null)
            {
                // add comma if there is more than one element
                if (list.Length != 1)
                    list += ", ";

                // add value to string
                list += pos.getValue();

                // move to next element
                pos = pos.getNext();
            }

            list += "]"; // close list

            return list;
        }

        public static void print<T>(Node<T> pos)
        {
            Console.Write(toString<T>(pos));
        }

        public static void println<T>(Node<T> pos)
        {
            Console.WriteLine(toString<T>(pos));
        }

        public static Node<int> createNumbersList(int start, int end, int step = 1)
        {
            if ((end - start) * step < 0) // if there's no way to reach the end with the step given
                return null;

            // initialize variables
            Node<int> first = null, // first element of the list
                        pos = null; // the current position

            int current = start;


            // while steps have not reached the destination
            while (
                    (end >= start && current <= end) ||
                    start > end && current >= end
                  )
            {
                if (first == null) // set first element if needed
                {
                    first = new Node<int>(current);
                    pos = first;
                }
                else
                {
                    pos.setNext(new Node<int>(current));
                    pos = pos.getNext();
                }

                current += step;
            }

            return first;
        }

        public static int listLength<T>(Node<T> list)
        {
            int counter = 0;

            Node<T> pos = list;

            while (pos != null)
            {
                counter++;
                pos = pos.getNext();
            }

            return counter;
        }
    }

}