判斷單鏈表中是否有環

public class HaveLoop {

	public static void main(String[] args) {
		
		Scanner scanner = new Scanner(System.in);
		String str = scanner.nextLine();
		char[] s = str.toCharArray();
		
		NodeList[] nodeLists = new NodeList[s.length];
		//初始化鏈表
		for(int i=0;i<s.length;i++){
			nodeLists[i] = new NodeList(s[i]);
		}
		
		//將鏈表連接起來
		for(int i=0;i<s.length;i++){
			if(i == s.length-1){
				//將單鏈表設置爲環
				nodeLists[i].next = nodeLists[0];
			}else {
				nodeLists[i].next = nodeLists[i+1];
			}
		}
		
		System.out.println(haveLoop(nodeLists[0]));
		
	}
	
	//判斷鏈表是否有環
	public static boolean haveLoop(NodeList nodeList){
		
		boolean flat = false;
		
		if(nodeList !=null && nodeList.next !=null){
			NodeList slow = nodeList;
			NodeList fast = nodeList;
			while (fast !=null && fast.next !=null) {
				slow = slow.next;
				fast = fast.next.next;
				if(slow == fast){
					//相遇則有環
					flat = true;
					break;
				}
			}
		}
		return flat;
	}

}