Why can't I sort a user defined LinkedList with this java code?

问题

I created a program in JAVA to add elements to a LinkedList and sort the elements while adding them. The swap technique I'm using in case of sorting is similar to that used while adding a node to the beginning of the LinkedList. The technique works in the latter case but fails to run in the former. I don't understand why this is not working. Below is my code for your reference.

//Node class
class Node{
    int d; Node link;
    Node(int d){
        this.d = d;
        link = null;
    }
}//Node

//LinkedList class
class LL{
    Node start;
    LL(){
        start = null; 
    }

    //method to add and sort the nodes 
    //in ascending order of the values of 'd' of the nodes
    void insert(Node nd){
        if(start==null){
            start = nd;
        }
        else{
            Node temp = start;
            while(temp!=null){
                if(nd.d<=temp.d){
                    Node t2 = temp;
                    temp = nd;
                    nd.link = t2;
                    break;
                }
                temp = temp.link;
            }
        }
    }//insert

    //method to display nodes of the LinkedList
    void display(){
        Node temp = start;
        do{
            System.out.print(temp.d + " ");
            temp = temp.link;
        }while(temp!=null);
    }//display
}//LL

//Main class
class LL_Test{
    public static void main(String[] args){
        LL myLL = new LL();
        myLL.insert(new Node(5));
        myLL.insert(new Node(2));
        myLL.insert(new Node(7));
        myLL.insert(new Node(6));
        myLL.insert(new Node(1));
        myLL.display();
    }//main
}//LL_Test

Expected output: 1 2 5 6 7
Obtained output: 5

回答1:

You never actually add a element except the first to the list. (temp = nd; does not set the link of the previous node to nd). You need to keep track of the previous node and add the new one after the element before the first one larger than the one you want to

void insert(Node nd) {
    Node temp = start;
    Node previous = null;

    while (temp != null && temp.d < nd.d) {
        previous = temp;
        temp = temp.link;
    }

    // insert node
    if (previous == null) {
        // insert at start
        nd.link = start;
        start = nd;
    } else {
        // insert somewhere in the middle
        nd.link = temp;
        previous.link = nd;
    }
}//insert

回答2:

Two comments, both applicable to insert(), start != null, inside the while(temp!=null) loop:

1. The condition is not quite right (I think) - for ascending order, you want to skip forward until you find a node with temp.d <= nd.d and either temp.link==null or temp.link.d >= nd.d.
2. In the body of the while loop in insert, you set nd.link so that the new node points to another node. However, you do not set temp.link=nd or anything similar to hook the new node into the chain that starts from start.

回答3:

My take on this :

void insert ( Node nd )
{
    Node temp = start;
    Node previous = null;
    while ( temp != null )
    {
        if ( nd.d <= temp.d )
        {
            nd.link = temp;
            if ( nd.d < start.d )
            {
                start = nd;
            }
            break;

        }
        previous = temp;
        temp = temp.link;
    }
    if( previous != null )
    {
        previous.link = nd;
    }
    if( start == null )
    {
        start = nd;
    }


}

来源：https://stackoverflow.com/questions/38461016/why-cant-i-sort-a-user-defined-linkedlist-with-this-java-code