Using recursive methods in Java
•
Java
For homework, I was asked to write an inclusion method for the custom linked list
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;
}
}
Solution
First, I like to do 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 the user's implementation details and prevents the list from being overwritten when the method is run
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