ListZipper.java

class ListZipperDemo {
  // arguments are passed using the text field below this editor
  public static void main(String[] args) {
    Node oneThruFive = new Node(1, new Node(2, new Node(3, new Node(4, new Node(5, null)))));
    Zipper zipper = new Zipper(null, oneThruFive);
    System.out.println(zipper.next().next().set(30).next().remove().insert(40).reconstruct());
  }
}

class Node {
  final int value;
  final Node next;
  
  Node(int value, Node next) {
    this.value = value;
    this.next = next;
  }
  
  @Override
  public String toString() {
    return "[" + value + ", " + next + ']';
  }
}

class Zipper {
  final Node beforeBackwards;
  final Node after;
  
  Zipper(Node beforeBackwards, Node after) {
    this.beforeBackwards = beforeBackwards;
    this.after = after;
  }
  
  Zipper next() {
    return new Zipper(new Node(after.value, beforeBackwards), after.next);
  }
  
  Zipper prev() {
    return new Zipper(beforeBackwards.next, new Node(beforeBackwards.value, after));
  }
  
  Zipper set(int value) {
    return new Zipper(beforeBackwards, new Node(value, after.next));
  }
  
  Zipper insert(int value) {
    return new Zipper(beforeBackwards, new Node(value, after));
  }
  
  Zipper remove() {
    return new Zipper(beforeBackwards, after.next);
  }
  
  Node reconstruct() {
    if (beforeBackwards == null) {
      return after;
    }
    return prev().reconstruct();
  }
}