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Thread: Please Help: Simple Double Linked List (remove, addBefore, )

  1. #1
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    Exclamation Please Help: Simple Double Linked List (remove, addBefore, )

    The code: #4887211 - Pastie

    import java.util.*;
    // use ListNode to represent the balls.
    class ListNode{
        protected int element;
        protected ListNode next= null;
        protected ListNode prev= null;
        public ListNode(int item, ListNode prev, ListNode next) {
            this.element = item;
            this.prev = prev;
            this.next = next;
        public ListNode(int item) {
            this.element = item;
        public int getElement(){return this.element;}
        public ListNode getNext(){return next;} 
        public ListNode getPrev(){return prev;} 
    class Result{
        // declare the member field
        private ListNode head = null;
        private ListNode tail = null;
        private ListNode current = null;
        private ListNode a = null;
        private int num_codes;
        // declare the constructor
        public Result(int num){
            num_codes= num;
            for(int i=1; i<num_codes+1;i++){
                /**        for(Listnode n = head; n!= null; n=n.next){
            public void print() throws NoSuchElementException {
                if (head == null)
                    throw new NoSuchElementException("Nothing to print...");
                ListNode ln = head;
                System.out.printf("List is: ");
                System.out.println(ln + " : "+ ln.getElement());
                for (int i=1; i < num_codes; i++) {
                    ln = ln.next;
                    System.out.println(" : " + ln.getElement());
            public void addLast(int i,int num_codes){
                        tail.next = new ListNode(i, null, null);
                        tail = tail.next;
                        System.out.print(" body ");
                        tail.next = new ListNode(i, null,tail);
                        tail = tail.next;}
                }else{// nothing in head
                    System.out.print(" head ");
                    head = new ListNode(i,null,null);// nothing before and after
                    tail = head;
            public boolean contains(int item) {
                for (ListNode n = head; n!= null; n=n.next)
                    if (n.getElement()==(item)) 
                        return true;
                return false;
            /* implement the operation for A
             *     PRE-Condition  :
             *     POST-Condition :
            public void doA(int x, int y) {
                ListNode current= null;
                ListNode a = null;
                for(ListNode ln=head;ln!= null;ln=ln.next){
                    System.out.println(" iteration " + ln.getElement());    
                        current  =ln;
                        a = ln;
                    //implement operation
                    //If already to the left to right
                    }else{// arrange it.
                        if(current!= null){
                            ListNode temp;
                                temp = current.prev;
                                current.prev.next = a;
                                current.prev = a;
                                a.next = current;
                                a.prev= temp;
                            }else{//if current is head
                                    current.prev = a;
                                    head = a;
                                    head.prev= null;
            /* implement the operation for B
             *     PRE-Condition  :
             *     POST-Condition :
            public void doB(int x, int y) {
            /* implement the operation for R
             *     PRE-Condition  :
             *     POST-Condition :
            public void doR(int x) {
                ListNode reme=null;
                for(ListNode m = head; m!=null; m=m.next){
                        reme = m;
                //execution of removing
                if(reme == null){
                    ;  //throw new NoSuchElementExeption("remove fails");
                        reme.next.prev= reme.prev;
                    }else{ //its a head
                        head = reme.next;
                        reme.prev= null;
                        reme.prev.next= reme.next;
                    }else{//its a tail
                        tail.next= null;
        public class Balls {
            public static void main(String[] args) {
                // declare the necessary variables    
                int num, ops;
                String task;
                // create new object from class Result;
                Result b1;
                // declare a Scanner object to read input
                Scanner myScanner = new Scanner(System.in);
                // read input and process them accordingly
                num = myScanner.nextInt();
                b1= new Result(num);
                ops = myScanner.nextInt();
                for(int i=0;i<ops;i++){
                    task = myScanner.next();
                    else if (task.equals("B")){
                        b1.doB(myScanner.nextInt(), myScanner.nextInt());
                    else if(task.equals("R")){

    There are N balls labelled with 1, 2, 3,..., N, from left to right.

    There are 3 kinds of operation.
    1. move the ball in position x before ball in position y, where x ≠ y. Reminder: if x is on the left of y, you may ignore this operation.

    2. move the ball in position x after ball in position y, where x ≠ y. Reminder: if x is on the right of y, you may ignore this operation.

    3. Remove the ball labelled x.

    Inputs are first the number of balls and then the number of operations.
    Then the type of operation(either A, B, R) and the position (x, y).

    myProblem is not being able to arrange he Ball and remove it. Can anyone take a look at my code and tell me what is wrong with it?
    Last edited by yeohv; September 30th, 2012 at 01:12 PM.

  2. #2
    Super Moderator curmudgeon's Avatar
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    Default Re: Please Help: Simple Double Linked List (remove, addBefore, )

    You should post your code in the forum rather than in a link. Use [code=java] [/code] tags too to allow your code to be readable.

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