Linked List Cycle - facebook code lab - wrong answer - still need to figure out, the code is not very efficient.

LinkedListCycle1.java

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     public int val;
 *     public ListNode next;
 *     ListNode(int x) { val = x; next = null; }
 * }
 */
public class Solution {
    /*
       1. if there is no cycle, return null
       2. if there is a cycle, use two runner, meet a same node; 
          and then, third runner starts from begining to meet the normal 
          runner at the beginning of cycle. 
    */
	public ListNode detectCycle(ListNode a) {
	    if(a == null)
	        return null; 
	    
	    ListNode normalRunner = a; 
	    ListNode doubleRunner = a; 
	    
	    while(normalRunner != null 
	    && doubleRunner != null
	    && normalRunner != doubleRunner)
	    {
	        normalRunner = normalRunner.next; 
	        if(doubleRunner.next == null)
	            return null; 
	        else
	            doubleRunner = doubleRunner.next.next; 
	    }
	    
	    //if(normalRunner == null)  // bug001 
	    if(normalRunner == null || doubleRunner == null)
	        return null; 
	    
	    ListNode thirdRunner = a; 
	    
	    while(thirdRunner != null 
	    && normalRunner != null 
	    && thirdRunner != normalRunner)
	    {
	        thirdRunner = thirdRunner.next; 
	        normalRunner = normalRunner.next; 
	    }
	    
	    return normalRunner; 
	}
}