public class AList {
  private ANode head = null;
  public String associate(String key, String value) {
    ANode n = nodeLookup(key);
    String oldValue;
    if (n != null) {
      oldValue = n.getValue();
      n.setValue(value);
    }
    else {
      n = new ANode(key, value, head);
      head = n;
      oldValue = null;
    }
    return oldValue;
  }
  public String find(String key) {
    ANode n = nodeLookup(key);
    return (n == null) ? null : n.getValue();
  }
  private ANode nodeLookup(String key) {
    ANode n = head;
    while (n!=null && !n.getKey().equals(key)) {
      n = n.getLink();
    }
    return n;
  }
  public int size() {
    ANode n = head;
    int length = 0;
    while (n!=null) {
      n = n.getLink();
      length++;
    }
    return length;
  }
}