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Thread: Sorting ascending/descending methods not working on double linked list

  1. #1
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    Default Sorting ascending/descending methods not working on double linked list

    Hi there. I'd like some help with the following code. I wrote displayAscending() and displayDescending() methods to this double linked list and it is not working at all. Logically it seems fine to me. I positioned the head in the beginning in the ascending method; created a variable named data1 as an auxiliar variable so it can store the values that are going to be moved; and moved the values. Same thing for the descending method but instead of the head I put the tail and move left the list, instead of right. I'd really appreciate some help because I've been stuck here for hours. Thank you

    import java.util.*;
     
    class node {
     
        int data;
        node left;
        node right;
     
        node(int d, node l, node r) {
            data = d;
            left = l;
            right = r;
        }
    }
     
    class Link {
     
        node head;
        node tail;
     
        public void insertfront(int data) {
            int flag = 0;
            node newnode = new node(data, null, null);
            if (head == null) {
                head = newnode;
                tail = head;
                tail.right = head;
                head.left = tail;
                flag = 1;
            } else {
                newnode.right = head;
                newnode.left = tail;
                tail.right = newnode;
                head = newnode;
                flag = 1;
            }
            if (flag == 1) {
                System.out.println("element " + data + "is inserted.");
            } else {
                System.out.println("element " + data + "is not inserted.");
            }
        }
     
        public void insertend(int data) {
            node newnode = new node(data, null, null);
            node current = head;
            while (current.right != head) {
                current = current.right;
            }
            current.right = newnode;
            newnode.left = current;
            newnode.right = head;
            tail = newnode;
        }
     
        public void insertatPosition(int data, int pos) {
            node newnode = new node(data, null, null);
            node current = head;
            node previous = head;
            int i = 1;
            while (i != (pos - 1)) {
                current = current.right;
                i++;
            }
            newnode.right = current.right;
            newnode.left = current;
            current.right = newnode;
            //current=current.right;  
        }
     
        public void display() {
            node current = head;
            do {
                System.out.print("     " + current.data);
                current = current.right;
            } while (current != head);
            System.out.println();
        }
     
        public void displayDescending() {
            node current = tail;
            int data1;
            while (current.left != null) {
                if (current.data > current.left.data) {
                    data1 = current.left.data;
                    current.left.data = current.data;
                    current.data = data1;
                    current = current.left;
                }
     
                System.out.println(current.data + "    ");
            }
            System.out.println();
        }
     
        public void displayAscending() {
            node current = head;
            int data1;
            while (current.right != null) {
                if (current.data > current.right.data) {
                    data1 = current.right.data;
                    current.right.data = current.data;
                    current.data = data1;
                    current = current.right;
                }
     
                System.out.println(current.data + "    ");
            }
            System.out.println();
        }
    }
     
    class Circular_Double {
     
        public static void main(String[] args) {
            Scanner scan = new Scanner(System.in);
            Link obj = new Link();
            while (true) {
                System.out.println("*******Please select the option.*********");
                System.out.println("\t1.Insert the element at first in the list."
                        + "\n\t2.Insert at element at end."
                        + "\n\t3.Insert element at certain positon."
                        + "\n\t4.Insert element at last."
                        + "\n\t5.Delete the element."
                        + "\n\t6.Search element."
                        + "\n\t7.display the Linked list."
                        + "\n\t8.display the Linked List ordered ascending"
                        + "\n\t9.display the Linked List ordered descending"
                        + "\n\t10.Exit from the program.");
     
                int num = scan.nextInt();
                switch (num) {
                    case 1:
                        System.out.println("Insert the element.");
                        int n = scan.nextInt();
                        obj.insertfront(n);
                        break;
                    case 2:
                        System.out.println("Insert the element.");
                        n = scan.nextInt();
                        obj.insertend(n);
                        break;
                    case 3:
                        System.out.println("Insert the element.");
                        n = scan.nextInt();
                        System.out.println("POSITION");
                        int p = scan.nextInt();
                        obj.insertatPosition(n, p);
                        break;
                    case 7:
                        obj.display();
                        break;
                    case 8:
                        obj.displayAscending();
                        break;
                    case 9:
                        obj.displayDescending();
                        break;
                    case 10:
                        System.exit(0);
                        break;
                    default:
                        System.out.println("U entered invalied data.So,enter valied data.");
                }
            }
        }
    }


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Sorting ascending/descending methods not working on double linked list

    it is not working at all.
    Can you post the print outs that show what is happening?
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Sorting ascending/descending methods not working on double linked list

    Let's suppose I inserted the number 4 and then the number 10. If I press number 8 to order it ascending, it gets into an infinite loop printing the number 10.

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Sorting ascending/descending methods not working on double linked list

    I inserted the number 4 and then the number 10. If I press number 8
    When I enter: 4 10 8 I (I put it in the Scanner constructor) I get this output:

    Running: java -client -cp . Circular_Double

    *******Please select the option.*********
    1.Insert the element at first in the list.
    2.Insert at element at end.
    3.Insert element at certain positon.
    4.Insert element at last.
    5.Delete the element.
    6.Search element.
    7.display the Linked list.
    8.display the Linked List ordered ascending
    9.display the Linked List ordered descending
    10.Exit from the program.
    U entered invalied data.So,enter valied data.
    *******Please select the option.*********
    1.Insert the element at first in the list.
    2.Insert at element at end.
    3.Insert element at certain positon.
    4.Insert element at last.
    5.Delete the element.
    6.Search element.
    7.display the Linked list.
    8.display the Linked List ordered ascending
    9.display the Linked List ordered descending
    10.Exit from the program.

    0 error(s)

    For testing I preload all of the Scanner input in its constructor:
            Scanner scan = new Scanner("4 10 8\n"); //System.in);

    A copy of the console would have shown me exactly what was entered on the keyboard. I need that for testing. I don't care to waste time responding to prompts and possibility entering the wrong value. Put it in the program and then it is always fast and easy and the same every time.
    If you don't understand my answer, don't ignore it, ask a question.

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