// Helene Martin, CSE 143
// A LinkedIntList object represents an ordered list of linked nodes.  
// Like ArrayIntList, LinkedIntList is an implementation of the List ADT.
public class LinkedIntList {
	private ListNode front;
	
	// Constructs an empty list.
	public LinkedIntList() {
		front = null;
	}

	// Add the given value to the end of the list.	
	public void add(int value) {
		if (front == null) {
			front = new ListNode(value);
		} else {
			// list wasn't empty; find the back
			// (note: this is inefficient.  We could keep a reference to the last node)		
			ListNode current = front;
			while (current.next != null) {
				current = current.next;
			}
			current.next = new ListNode(value);
		}
	}
	
	// Returns the value at a given index
	// pre: 0 <= index < number of nodes; front != null
	// throws 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;
	}
	
	// Adds a value at a given index.
	// pre: 0 <= index <= size
	// Throws a NullPointerException if index > size.
	public void add(int index, int value) {
		if (index == 0) {
			front = new ListNode(value, front);
		} else {
			ListNode current = front;
			for (int i = 0; i < index - 1 ; i++) {
				current = current.next;
			}
			ListNode temp = new ListNode(value, current.next);
			current.next = temp;
			// also ok:	current.next = new ListNode(value, current.next);
		}
	}
	
	// Returns a comma-separated String representation of this list.
	public String toString() {
		if (front == null) {
			return "[]";
		} else {
			String result = "[" + front.data;
			ListNode current = front.next;
			while (current != null) {
				result += ", " + current.data;
				current = current.next;
			}
			result += "]";
			return result;
		}
	}
}