我尝试使用Google搜索。 DoublyLinkedList问题。 编辑（2）

Question

I am new to LinkedLists. We are working with DoublyLinkedLists and we have to do a method called addAfter. So I googled it and came up with nothing. The node class and variable initialation is given to us in a skeleton by him as well, so right away I am thinking, am I missing an initialation for newInfo and afterThis?. This is how he describes addAfter---

This method adds a new node containing the integer newInfo to the next of the node containing the integer afterThis. If there is no node containing the integer afterThis, insert the new node at the last. If there are multiple nodes containing the integer afterThis, insert the new node right next to the first occurrence of afterThis in the list.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;



//import DoublyLinkedList.Node;



public class DoublyLinkedList {
    public static class Node {
        private int element;
        private Node prev, next;


        public Node(int e, Node p, Node n) {
            element = e;
            prev = p;
            next = n;
        }

        public  int getElement() {
            return element;
        }

        public Node getPrev() {
            return prev;
        }

        public Node getNext(){
            return next;
        }

        public void setPrev(Node p) {
            prev = p;
        }

        public void setNext(Node n) {
            next = n;
        }


    }
/***************************************************************************************************************************/   
    public DoublyLinkedList(String fileName) throws IOException {

        FileReader input = new FileReader(fileName); // this is where it reads the filenames HW4-A and myAnotherInput
        BufferedReader myReader = new BufferedReader(input);
        String line = "";

        while ((line = myReader.readLine()) != null) {
            int nextNumber = Integer.parseInt(line.trim());//needed trim or it kept throwing an error. Suggested by Liam.
            // System.out.println(nextNumber);
            addLast(nextNumber); // takes the number given by parseint and puts it last
            System.out.println(nextNumber);
        }
        input.close();


    }
    private Node header;
    private Node trailer;
    private int size = 0;

    public DoublyLinkedList() {
        header = new Node(0, null, null);
        trailer = new Node(0, header, null);
        header.setNext(trailer);

    }



    public String toString() {
        String toReturn = "";

        Node current = header;


        while (current != null) {
            toReturn += current.getElement();//Credit to Liam (do not know last name, a CS student friend)
            current = current.getNext();

            if (current == null) {
                break;
            } else {
                toReturn += " -> "; // Allows for -> to be put in between the numbers 

            }

        }

        return toReturn;
    }



    public void reverseList() {
        // complete this method
    }

    public void addAfter(int newInfo, int afterThis) {
        Node tmp = new Node(newInfo,header.next, trailer.prev);
    tmp.prev = header.next;
    header.next = header;
    tmp.next = header.next;

    if(afterThis == null)
        newInfo.addLast();
    }

    public void negateList() {
        // complete this method
    }


    public void addFirst(int e) {
        Node tmp = new Node(e, header, null);
        if(header != null ) {header.prev = tmp;}
        header = tmp;
        if(trailer == null) { trailer = tmp;}
        size++;
    }

    public void addLast(int e) {

        Node tmp = new Node(e, null, trailer);
        if(trailer != null) {
            trailer.next = tmp;
            }
        trailer = tmp;
        if(header == null) {
            header = tmp;


        size++;
        }
}

    public int size() {
        return size;//line 39 size
    }

    public boolean isEmpty() {
        return size == 0;
    }

}

this is what I have so far. Again,I just need a little guidance on the addAfter. I appreciate any education with LinkedLists because they are proving a hard thing for me to grasp. Thanks!

Answer 1

Think about this logically, a double linked list is a series of nodes that looks like:

How would we go about adding something after B, but before C?

1. Take our new item, and set it to b's next and C's prev.
2. Take B and set it to our item's prev.
3. Take C and set it to our items's next.

There is also the special case, where you are adding after D or the last element in the list. In this situation you simply set D's next, and the new item's prev.