//compiler options: /t:library
using System;

public class List<T> {
  public T info;
  public List<T> next;
  
  public List(T n, List<T> nxt) {
    info = n;
    next = nxt;
  }

  public static void Write(List<T> p) {
    if(p == null) {
      Console.WriteLine("null");
    }
    else {
      do {
        Console.WriteLine(p.info);
        p = p.next;
      } while(p != null);
    }
  }

  public static int Length(List<T> p) {
    int br = 0;
    while(p != null) {
      br++;
      p = p.next;
    }
    return br;
  }

  public static List<T> FromArray(T[] a) {
    int n = a.Length;
    if(n == 0) { return null; }
    List<T> p = null;
    for(int i = n - 1; i >= 0; i--) {
      p = new List<T>(a[i], p);
    }
    return p;
  }

  public static bool Equal(List<T> p, List<T> q) {
    while(p != null && q != null) {
      if(!Object.Equals(p.info, q.info)) { break; }
      p = p.next;
      q = q.next;
    }
    return p == null && q == null;
  }

  public static List<T> Copy(List<T> p) {
    if(p == null) { return null; }
    List<T> first = new List<T>(p.info, null);
    List<T> last = first;
    p = p.next;
    while(p != null) {
      last.next = new List<T>(p.info, null);
      last = last.next;
      p = p.next;
    }
    return first;
  }
  
  public static T[] ArrayFrom(List<T> p) {
    // zahtevamo da je lista p neprazna
    int n = Length(p);
    T[] a = new T[n];
    for(int i = 0; i < n; i++) {
      a[i] = p.info;
      p = p.next;
    }
    return a;
  }

  public static List<T> Rev(List<T> p) {
    if(p == null || p.next == null) { return p; }
    List<T> q = p.next;
    p.next = null;
    List<T> r;
    do {
      r = p;
      p = q;
      q = q.next;
      p.next = r;
    } while(q != null);
    return p;
  }
}