java - 在 Java 中对双链表进行排序

Question

我必须为我的编程课制作一个链表程序。它可以工作，每次插入一个数字时，它都会放在列表的开头。现在我的老师希望我们使用链表程序并按升序对数字进行排序。我完全不知道如何做到这一点。任何人都可以指出我正确的方向吗？
这是我的列表代码:

public class SortedList {

private DoubleNode head = null;
private int listLength;

public static void main(String[] args) {
    SortedList list = new SortedList();
    list.insert(6);
    list.insert(7);

    System.out.println(list.toString());

}

public void insert(double value) {

    head = new DoubleNode(value, head);
    listLength++;

}

public String toString() {

    String answer = "[ ";
    for (DoubleNode current = head; current != null; current = current
            .getLink()) {
        answer += current.getData() + " ";
    }
    answer += "]";
    return answer;
}

public int find(double value) {
    if (listLength == 0)
        return -1;

    int pos = 1;
    for (DoubleNode current = head; current != null; current = current.getLink()) {
        if (current.getData() == value)
            return pos;
        pos++;
    }
    return -1;
}

public int size() {
    return listLength;
}

public boolean removeAt(int index) {
    if (index < 1 || index > listLength)
        return false;

    if (index == 1) {
        if (head != null) {
            head = head.getLink();
            listLength--;
        }
        return true;
    }

    DoubleNode current = head;
    for (int i = 1; i < (index - 1); i++) {
        if (current.getLink() == null)
            return false;
        current = current.getLink();
    }
    current.setLink(current.getLink().getLink());
    listLength--;
    return true;
}

}

这是我的老师给出的节点的代码:

// File: DoubleNode.java based on the DoubleNode class by Michael Main

/**************************************************************************
* DoubleNode provides a node for a linked list with double data in each node.
*
* @note
*   Lists of nodes can be made of any length, limited only by the amount of
*   free memory in the heap. 
*
* @author Michael Main 
*   shortened by Beth Katz and Stephanie Elzer to be only the basics
*
* @version
*   February 2007
***************************************************************************/
public class DoubleNode
{
// Invariant of the DoubleNode class:
//   1. The node's double data is in the instance variable data.
//   2. For the final node of a list, the link part is null.
//      Otherwise, the link part is a reference to the next node of the list.
   private double data;
   private DoubleNode link;   

/**
* Initialize a node with a specified initial data and link to the next
* node. Note that the initialLink may be the null reference, which 
* indicates that the new node has nothing after it.
* @param initialData
*   the initial data of this new node
* @param initialLink
*   a reference to the node after this new node--this reference may be 
*   null to indicate that there is no node after this new node.
* @postcondition
*   This node contains the specified data and link to the next node.
**/   
public DoubleNode(double initialData, DoubleNode initialLink)
{
  data = initialData;
  link = initialLink;
}

/**
* Accessor method to get the data from this node.   
* @param - none
* @return
*   the data from this node
**/
public double getData( )   
{
  return data;
}

/**
* Accessor method to get a reference to the next node after this node. 
* @param - none
* @return
*   a reference to the node after this node (or the null reference if 
*   there is nothing after this node)
**/
public DoubleNode getLink( )
{
  return link;                                               
} 

/**
* Modification method to set the data in this node.   
* @param newData
*   the new data to place in this node
* @postcondition
*   The data of this node has been set to newData.
**/
public void setData(double newData)   
{
   data = newData;
}                                                               

/**
* Modification method to set the link to the next node after this node.
* @param newLink
*   a reference to the node that should appear after this node in the 
*   linked list (or the null reference if there is no node after this node)
* @postcondition
*   The link to the node after this node has been set to newLink. Any other 
*   node (that used to be in this link) is no longer connected to this node.
**/
public void setLink(DoubleNode newLink)
{                    
  link = newLink;
}  
}

Answer 1

想法

1) 在最简单的情况下，列表已经排序:

-> A

2)现在，考虑“下一个”情况(即向大小为 1 的列表中添加 1 个新元素)

-> A [now, i am going to try adding C]

您可以简单地检查 C 是否 > 比 A，在这种情况下，您在末尾添加“C” (->A->C)

3)我们可以概括情况(2):在任何后续情况下，您都必须沿着列表向下走，直到您“看到”一个新节点，该节点大于您插入的节点。

-> A -> C [adding B]

check 1: A (B > A)
check 2: C (B < C) ! 

这意味着我们可以按如下方式替换链接:

replace A -> C with 2 new links, 1 from A -> B , and also another from B -> C.

以这种方式插入保证您的列表保持排序。

具体

因此，您必须修改应用程序的 insert(..) 方法，从列表的开头开始，检查每个 DoubleNode，向下走，并“记住”即存储前一个 DoubleNode，直到它到达末尾列表的 --- OR 它看到最后一个节点 < 比新节点，而当前节点 > 比新节点。