// CSE 143, Winter 2011, Marty Stepp                                            
// A LinkedIntList object stores a list of integers using a series of linked                                         
// node objects.  We will implement the same methods as ArrayIntList.                                              
                                           
public class LinkedIntList {                                     
    private ListNode front;   // refers to first node in list (null if empty)                                    
                               
    // Constructs a new empty list.                                            
    public LinkedIntList() {                                         
        front = null;  // null front means empty                                                   
    }                                                    
                                                   
    // Adds the given value to the end of this list.                               
    public void add(int value) {                                 
        if (front == null) {                                                  
            // empty list                                     
            front = new ListNode(value);                               
        } else {                                       
            // non-empty list; walk to last node                                               
            ListNode current = front;                                         
            while (current.next != null) {                                              
                current = current.next;                                       
            }                               
                                                    
            // add new node at end of list                                               
            current.next = new ListNode(value);                               
        }                                        
    }                                                     
                                                  
    // Inserts the given value into this list at the specified index.                                                    
    // Precondition: 0 <= index <= size                               
    // Throws a NullPointerException if index > size.                                                         
    public void add(int index, int value) {                                               
        if (index == 0) {                                                     
            // insert at front of list                                                  
            front = new ListNode(value, front);                               
        } else {                                  
            // walk to node before the one to insert                                                  
            ListNode current = front;                                 
            for (int i = 0; i < index - 1; i++) {                                         
                current = current.next;                                              
            }
            
            ListNode newNode = new ListNode(value, current.next);
            current.next = newNode;
            
            // shorter version of the above code
            // current.next = new ListNode(value, current.next);
        }
    }
    
    // Returns the element at the specified index from the list.
    // Precondition: 0 <= index < size
    // Throws a NullPointerException if index >= size.
    public int get(int index) {
        ListNode current = front;
        for (int i = 0; i < index; i++) {
            current = current.next;
        }
        return current.data;
    }
}