替换链接列表中的项目并进行排序

Question

所以我在替换链表中的项目时遇到问题，因为我正在同时添加和排序。例如，我想插入数字2,7,3所以在执行期间，当我插入3时，我最终用7交换它，所以列表看起来像：2,3,7。但是现在我的代码在交换价值的时候就挂了。

    public void ADD(E num) {
    Node<E> temp = new Node<>(num);
    if (this.head == null) {
        this.head = temp;
        System.out.println("Was empty");
    } else {


        Node<E> lead = this.head;
        Node<E> tail = this.head;

        while (lead != null) {

            if (lead.info.compareTo(temp.info) == -1) {//If the lead.info is less than the argument then -1 is returned.

                lastNode().next = temp; // adds to the end of linked list
                //System.out.println("it works");

            } 
            if (lead.info.compareTo(temp.info) == 1) { //if the greater than we swap out

                Node<E> z = lead;
                lead = temp;
                lastNode().next = lead;
                lead=lead.next;

            }
            lead=lead.next;

        }
    }

}

Answer 1

添加一个添加到前面的案例，保留一个prev引用（看起来你正在使用lastNode()，但它的工作方式并不明显）。

要添加到最后，除了检查最后一个值是否小于插入的值之外，还要检查if (lead.next == null)以确保您位于列表的末尾。

它应该是这样的：

 public void ADD(E num) {
    Node<E> temp = new Node<>(num);
    if (this.head == null) {
        this.head = temp;
        System.out.println("Was empty");
    } else {


        Node<E> lead = this.head;
        Node<E> prev = null; //modified

        //first check if it should be added at the front
        if (lead.info.compareTo(temp.info) == 1) { 
           temp.next = this.head;
           this.head = temp;
           System.out.println("added to front of list");
           return;
        }

        while (lead != null) {

            //if (lead.info.compareTo(temp.info) == -1) {//If the lead.info is less than the argument then -1 is returned.
            if (lead.next == null && lead.info.compareTo(temp.info) == -1){ //if at the end of the list and lead.info is less than the argument, add to the end

                //lastNode().next = temp; // adds to the end of linked list
                lead.next = temp;
                System.out.println("added to end of list");
                return; //return if node was added

            } 
            if (lead.info.compareTo(temp.info) == 1) { //if the greater than we swap out

                //Node<E> z = lead;
                prev.next = temp;
                temp.next = lead;
                //lead = temp;
                //lastNode().next = lead; //not needed if you use prev
                //lead=lead.next;
                System.out.println("added inside of list");
                return; //return if node was added

            }
            prev = lead; //added this, keep prev one behind lead
            lead=lead.next;

        }
    }

}