CODEWITHSUNDEEP
java
jorgeAChacon
jorgeAChacon

Reputation: 327

Using Recursive method in java

for homework I was asked to write a contain method for a custom linked list. I know that the recursive method should have a base case and then the recursive case.However, I am having some trouble understanding how to write the recursive case of the method. So far this is what I have written, but my code is executing the base case more than once. Can you please give me some guidance?

public class OrderedList {

private Node first;

//Constructor
public OrderedList() {
    this.first = null;
}

//Return the number of items in the list
public int size() {
    int counter = 0;
    Node pointer = this.first;
    while (pointer != null) {
        counter++;
        pointer = pointer.next;
    }
    return counter;
}

//Return an array of copies of the stored elements
public Comparable[] getStore() {

    Comparable[] elements = new Comparable[size()];
    Node pointer = this.first;
    if (this.first == null) {
        return elements;
    } else {
        int i = 0;
        while (pointer != null) {
            elements[i] = pointer.data;
            pointer = pointer.next;
            i++;
        }
        return elements;
    }

}
//true iff item matches a stored element
//Recursive

public boolean contains(Comparable item) {

    //Base case
    if (this.first == null) {

        return false;
    }
    Node pointer = this.first;
    this.first = this.first.next;

    if (pointer.data.compareTo(item) == 0) {

        return true;

    } 
    //Recursive case

    else {

        boolean info = contains(item);
        pointer.next = this.first;
        this.first = pointer;

        return info;
    }
}

Upvotes: 5

Views: 1348

Answers (3)

jfc8192
jfc8192

Reputation: 1

From what I am seeing, your code will return true once the else statemnet have been executed once. I think what you need to do is to set the boolean value to false everytime because recursion acts very much like a while loop and if the values are not updated, the base case would be executed over and over again.

Upvotes: 0

Ted Hopp
Ted Hopp

Reputation: 234857

To implement a recursive solution, you need an auxiliary method for contains. The auxiliary method should have an additional argument that is the Node from which to start testing. The public contains method should call the auxiliary method and pass this.first as the start node. The rest of the logic should then be pretty simple for you to figure out.

Upvotes: 0

thatidiotguy
thatidiotguy

Reputation: 9011

First of all I like to do something like this:

public boolean contains(Comparable item)
{
     return containsHelper(this.first, Comparable item);
}

private boolean containsHelper(Node node, Comparable item)
{
    //base case
    if(node == null)
    {   
         return false;
    }
    else
    {
         if(node.data.compareTo(item) == 0)
         {
             return true;
         }

         return containsHelper(node.next, item);
    }


}

This hides implementation details from the user and it stops your list from getting overridden when you run that method.

Upvotes: 3

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