Question

I am trying to create a data structure to hold polynomials. So far i have created a Node class to store the data like so : (Coefficient, exponent, link to next node)
I am running into problems when trying to add two lists together though. My method adds the first values in each of the lists but then terminates.

here is my code below:

    public class Node{

//Fields
public int data1;
public int data2;
public Node next;



//constructors
public Node(){
    data1 = 0;
    data2 = 0;
    next = null;
}


public Node(int d1){
    data1 = d1;
    data2 = 0;
    next = null;
}

public Node(int d1, Node n){
    data1 = d1;
    data2 = 0;
    next = n;
}

public Node(int d1, int d2){
    data1 = d1;
    data2 = d2;
    next = null;
}
public Node(int d1,int d2, Node n){
    data1 = d1;
    data2 = d2;
    next = n;
}

//Methods

//Fetch data
public int getData1(){
    return data1;
}

public int getData2(){
    return data2;
}

//store Data
public void setData1(int d){
    data1 = d;
}

public void setData2(int d){
    data2 = d;
}

public void addData1(Node n2){
    data1 = data1 + n2.data1;
}

//getNext
public Node getNext(){
    return next;
}

//Get data of next node
public int getNextData1(){
    return next.data1;
}

public int getNextData2(){
    return next.data2;
}

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

public boolean containsLink(){
    if(this.next != null){
        return true;
    }else{
        return false;
    }
}

public static void displayAll(Node head){
    for( ; head != null; head = head.next ){
        System.out.printf("%d, %d\n", head.data1, head.data2);
    }
}

public static int numOfNonZeroData1(Node n){
    int count = 0; 
    for( ; n != null ; n = n.next ){
        if(n.data1 != 0){
            count++;
        }
    }
    return count;
}

public static int numOfNonZeroData2(Node n){
    int count = 0; 
    for( ; n != null ; n = n.next ){
        if(n.data2 != 0){
            count++;
        }
    }
    return count;
}

public static int listLength(Node head){
    int counter = 0;
    for(; head!=null; head = head.next){
        counter++;
    }
    return counter;
}

public static void toPolynomial(Node head){
    int order = Node.listLength(head);
    int i = 0;
    int increment = Node.numOfNonZeroData2(head);
    //sortList(head);
    for( ; head != null; head = head.next){
        if(head.data2 != 0){
            if(i >= 0 && i < order){
                System.out.printf("%dx^%d", head.data1, head.data2);
                i++;
                if(i < increment && head.data1 >= 0){
                    System.out.print("+");      //case integer is positive
                }else if(i != increment && head.data1 <= 0){
                    System.out.println(" ");    //case integer is negative
                }
            }

        }
    }
    System.out.println();
}




public static Node mergeLists(Node n1, Node n2){
    if ( n1 == null) 
        return n2;
    else if ( n2 == null) 
        return n1;
    else {
        n1.next = mergeLists( n1.next, n2 );     // Note how we exchange p and q here
        return n1;
    }
}









public static Node addPolynomials(Node n1, Node n2){
    for( ; n1 != null; n1 = n1.next){
        for(; n2 != null; n2 = n2.next){
            if(n1.getData2() == n2.getData2()){
                n1.addData1(n2);
                System.out.println("added " + (n1.data1 - n2.data1) + " and " + n2.data1 );
            }

        }

    }
    return n1;
}

public static void subtractPolynomials(Node n1, Node n2){

}

public static void multiplyPolynomials(Node n1, Node n2){

}
 }

and the main method:

    public class LinkedListsMain {


public static void main(String[] args) {

    Node head;
    Node head2;

    head = new Node(5,  1, new Node(7, 4,  new Node(9 ,5, new Node(12, new Node (15)))));
    head2 = new Node(3, 1, new Node(1, 4, new Node(29, 5)));
    Node.displayAll(head);
    Node.displayAll(head2);
    System.out.println("Length: " + Node.listLength(head));
    System.out.println("Length: " + Node.listLength(head2));
    Node.toPolynomial(head);
    Node.toPolynomial(head2);
    //Node.mergeLists(head, head2);
Node.addPolynomials(head, head2);
    System.out.println("Add completed");
    Node.toPolynomial(head);
}

}

Any ideas?

To give more information, I am using linked lists as a more efficient data structure. I am inputting two linked lists and trying to add the corresponding elements together. I will enclose my entire code!

for example: if the input is
5x^1+7x^4+9x^5 + 3x^1+1x^4+29x^5

i would like the program to output
8x^1+8x^4+38^5

Answer 1

From what I got from your question, the problem is that when your outer loop is executed 2nd time, then n2 has already reached its last position.

Because, you haven’t re-initialized n2 in inner loop again.
So, it is null as from the first iteration. So your outer loop would run only once.

Try changing your method with the below one: –

public static Node addPolynomials(Node n1, Node n2) {
    Node x = n1;
    Node y = n2;

    for(x = n1; x != null; x = x.next){
        for(y = n2; y != null; y = y.next){
            if(x.getData2() == y.getData2()){
                x.addData1(y);
                System.out.println("added " + (x.data1 - y.data1) + " and " + y.data1);
            }

        }
    }

    return x;
}