Remove some chars from a singly-linked list of chars using a backtracker.

BacktrackingCharFiltering.java

class BacktrackingCharFiltering {

  static class Node<E> {
    Node<E> next;
    E data;

    Node(E data) {
      this.data = data;
    }
  }
  
  static class List<E> {
    Node<E> head;
    Node<E> tail;
    
    //inserts at tail
    void insert(Node<E> newNode) {
      if (head == null) {
        head = newNode;
        tail = newNode;
      }
      else {
        tail.next = newNode;
        tail = newNode;
      }
    }
    
    List<E> remove(Set<E> rLetters) {
      Node<E> backTracker = null;
      Node<E> nodePtr = head;
      
      while (nodePtr != null) {
        if (rLetters.contains(nodePtr.data)) {
          if (backTracker != null) { //we're ahead in list
            backTracker.next = nodePtr.next;
            nodePtr = nodePtr.next;
          }
          else { //we're on the head
            head = nodePtr.next;
            nodePtr = head;
          }
        }
        else {
          backTracker = nodePtr;
          nodePtr = nodePtr.next;
        }
      }
      
      return this;
    }
  }

  public static void main(String[] args) {
    List<Character> letters = new List<>();
    Set<Character> rLetters = new HashSet<>();
    
    String rString = "strwk";
    for (int i = 0; i < rString.length(); i++) {
      rLetters.add(rString.charAt(i));
    }
    
    String word = "star trek: wrath of khan";
    for (int i = 0; i < word.length(); i++) {
      letters.insert(new Node<>(word.charAt(i)));
    }
    
    letters.remove(rLetters);

    Node<Character> begin = letters.head;
    while (begin != null) {
      System.out.print(begin.data + " --> ");
      begin = begin.next;
    }
  }
}