Reputation: 57
I implemented a solution to reverse a linked list in java that I found online. But it is not working in my code for some reason.
When I print the list it only prints the first node. I know the print method works because it prints the whole thing when I don't try to reverse.
Where did I go wrong in this code?
public class LinkedLists {
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.addLast(10);
list.addLast(20);
list.addLast(30);
list.reverseList();
list.print();
}
public static class LinkedList{
private class Node{
private int value;
private Node next;
}
public Node first;
public Node last;
public void addLast(int item){
Node node = new Node();
node.value = item;
if(first == null) {
first = node;
last = node;
} else {
last.next = node;
last = node;
}
}
private Node reverse(Node head, Node newHead) {
//base case: when first = last you return
if(head == null) {
return newHead;
}
Node temp = head.next;
head.next = newHead; //this will initially be null
newHead = head;
head = temp;
return reverse(head, newHead);
}
public Node reverseList() {
return reverse(first, null);
}
public void print(){
Node current = first;
while (current != null){
System.out.print(current.value + " ");
current = current.next;
}
}
} //class ends
}
Upvotes: 0
Views: 77
Reputation: 351403
Although reverse
returns the correct reference for the new head, the initial call of reverseList
-- in the main program -- ignores this returned reference.
Your reverseList
method should better not return anything, but instead update the first
and last
members:
public void reverseList() {
last = first;
first = reverse(first, null);
}
Upvotes: 2