Linked List Cycle - facebook code lab - pass all test cases - no nested while loop

LinkedListCycle3.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. 
       study the code: 
       https://siddontang.gitbooks.io/leetcode-solution/content/linked_list/linked_list_cycle.html
    */
	public ListNode detectCycle(ListNode a) {
	    if(a == null || a.next == null) {
            return null;
        }

        ListNode fast = a;
        ListNode slow = a;

        boolean foundLoop = false; 
        while(fast.next != null && fast.next.next != null) {
            fast = fast.next.next;
            slow = slow.next;
            if(fast == slow) {
               foundLoop = true; 
               break; 
            }
        }

        if(!foundLoop)
            return null;
        
        // stil use fast slow two pointers, but need to move one step
        slow = a; 
        while(slow != fast)
        {
           slow = slow.next; 
           fast = fast.next; 
        }
        return slow; 
	}
}