How to know if a custom Java Node is included in a second Node?

Question

I need some help with Java again... I have this simple custom Node class:

class Node{
    private int elem;
    private Node next;

    public Node(int elem, Node next){
        this.elem = elem;
        this.next = next;
    }

    public int getElem(){
        return elem;
    }

    public void setElem(int elem){
        this.elem = elem;
    }

    public Node getNext(){
        return next;
    }

    public void setNext(Node next){
        this.next = next;
    }
}

I need to implement a static boolean method which takes two nodes as parameter and returns true if all elements of first Node are contained in second Node. Example Output:

        1) Node p {5} Node q {5,5} returns true since element 5 of Node p is also in Node q
        2) Node p {1,3,5} Node q {0,1,2,3,4,5} returns true since 
        all elements of Node p are also in Node q
        3) Node p {5,3} Node q {3,4,6} returns false because 
        element 5 of Node p is not in Node q
        4) If first Node given as parameter to method is empty
        (with no values), the method will return true.

This is my idea:

public static boolean included(Node p, Node q){
        //every element in p is in q?
        int count = 0;
        int temp = 0;
        int length = 0;
        while(p != null){
            temp = p.getElem();
            length++;
            while(q != null){
                if(q.getElem() == temp)
                    count++;
                q = q.getNext();
            }
            p = p.getNext();
        }
        return length == count || p == null;
    }

For every element of Node p i must check if is also in Node q. If true, I increment an integer I called count, else I do nothing. Once this check is done on all p elements, I check if count == size of Node p or Node p is empty aka null

Problem is: this method always returns true. I tried to remove p == null from return value and something changed, so I suspect that's the issue so I show you how I create Nodes:

        Node p = null;
        Node q = null;
        int arr1[] = {5,4,3,2,1,0};
        int arr2[] = {5,3,1};
        for(int i = 0; i < arr1.length; i++)
            p = new Node(arr1[i], p);
        for(int i = 0; i < arr2.length; i++)
            q = new Node(arr2[i], q);

With those Nodes I should get true, but I get it only where instruction p == null is included in return value of method.

How would you guys implement method? Hope I've been clear. Thank you very much

That is... a strange way to implement a List. Normally, one would not operate on the Nodes directly, but on the list and one would impelment some public boolean containsAll(List that) for this functionality — Turing85
– Turing85, Commented Jun 22, 2018 at 17:12

sprinter · Accepted Answer · 2018-06-22 17:16:04Z

2

Consider these lines of your code:

    while(p != null){
        ...
    }
    return ... || p == null;

Clearly this is always going to return true because p is always null when the loop exits.

I would suggest you implement the logic in two methods. The first checks if a node or its successors contain an element. The second checks all elements with the second node.

boolean hasElement(int elem) {
    return this.elem == elem || (next != null && next.hasElement(elem));
}

boolean hasAllElements(Node node1, Node node2) {
    return node2.hasElement(node1.elem) && (next == null || hasAllElements(next, node2));
}

answered Jun 22, 2018 at 17:16

sprinter

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