LinkedSet.java

class LinkedSet<T> {
    private class Node<T> {
        private T item;
        private Node<T> next;
        
        Node(T item0, Node<T> next0) {
            item = item0;
            next = next0;
        }
    }
    
    private Node<T> head = null;
  
    public int size() {
      Node<T> p = head;
      int numItems = 0;
      while(p!=null) {
        numItems++;
        p = p.next;
      }
      return numItems;
    }
    
    public boolean add(T t) {
      if(contains(t)) return false;
      head = new Node<T>(t,head);
      return true;
    }

    public boolean contains(T t) {
      Node<T> p = head;
      while(p!=null && !equals(p.item,t)) {
        p = p.next;
      }
      return p!=null;
    }
    
    public boolean remove(T t) {
      Node<T> p =head;
      Node<T> pPred = null;
      while(p!=null && !equals(t,p.item)) {
        pPred = p;
        p=p.next;
      }
      if(p==null) return false;
      if(p==head) head = head.next;
      else pPred.next = p.next;
      return true;
    }
    
    private boolean equals(T t1, T t2) {
      if(t1!=null) return t1.equals(t2);
      else return t2==null;
    }
}