输出单链表的中间节点

输入一个单向链表，如果该链表的结点数为奇数，输出中间的结点；如果链表结点数为偶数，输出中间两个结点前面的一个。

public class Test_09_extend {

	
	public static void main(String[] args) {
		SignalList list= new SignalList();
		int[] input = {1,2,3,4,5,6,7,8,9};
		for(int i =0;i<input.length;i++){
			list.add(input[i]);
			}
		if(findMiddle(list)==null){
			System.out.println("结果为空！");
			return ;
		}
		System.out.println(findMiddle(list).getKey());
	}

	public static Node findMiddle(SignalList list){
		if(list == null){
			return null;
		}
		Node fast = list.getHead();
		Node slow = list.getHead();
		while(fast.getNext()!=null&&fast.getNext().getNext()!=null){
			fast = fast.getNext().getNext();
			slow = slow.getNext();
		}
		return slow;
	}

	
}

class Node{
	private int key;
	private Node next;
	public int getKey() {
		return key;
	}
	public void setKey(int key) {
		this.key = key;
	}
	public Node getNext() {
		return next;
	}
	public void setNext(Node next) {
		this.next = next;
	}
	
	
}
class SignalList{
	Node head ;
	Node tail;
	public Node getHead() {
		return head;
	}

	public void setHead(Node head) {
		this.head = head;
	}

	public int getSize() {
		return size;
	}

	public void setSize(int size) {
		this.size = size;
	}

	int size=0;
	
	public void add(int i){
		Node newnode = new Node();
	    newnode.setKey(i);
		if(size == 0){
			
		    head = newnode;
		    tail = newnode;
		    size++;
		}
		else{
			tail.setNext(newnode);
			tail = newnode;
			size++;
		}
	}
	
}

输出结果：5