Remove duplicate in sorted linked list - facebook code lab - stack overflow issue - first practice

EMDUPLNK1.java

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     public int val;
 *     public ListNode next;
 *     ListNode(int x) { val = x; next = null; }
 * }
 */
public class Solution {
	public ListNode deleteDuplicates(ListNode a) {
	    if(a==null)
	        return null; 
	  
	    if(a.next == null)
	        return a;
	   
	    if(a.val == a.next.val)
	    {
	        a.next = a.next.next;
	        return deleteDuplicates(a); 
	    }
	    else
	    {
	        a.next = deleteDuplicates(a.next); 
	        return a;
	    }
	}
}