public LinkNode find(int id) {
   LinkNode node = firstNode;
   // 循环递归查找
   while (node.getId() != id) {
     if (node.getNext() != null) {
       node = node.getNext();
     } else {
       return null;
     }
   }
   return node;
 }
  public LinkNode remove(int id) {
    LinkNode needDelete = firstNode;
    LinkNode previNode = firstNode;
    while (needDelete.getId() != id) {
      if (needDelete.getNext() == null) {
        return null;
      } else {

        previNode = needDelete;
        needDelete = needDelete.getNext();
      }
    }

    if (needDelete.equals(firstNode)) {
      firstNode = firstNode.getNext();
    } else {
      previNode.setNext(needDelete.getNext());
    }

    return needDelete;
  }