删除单向链表指定节点

给定单向链表的一个头指针和节点指针，定义一个函数在O(1)时间删除该节点。

public class ListNode {
    public int value;
    public ListNode next;
}
public class Test {
    public void test(ListNode headNode, ListNode targetNode) {
        if (headNode == null || targetNode == null) {
            return;
        }
        if (headNode == targetNode) {//目标节点是头节点
            headNode = headNode.next;
            return;
        }
        if (targetNode.next == null) {//目标节点是尾节点
            ListNode tmp = head;
            while(tmp.next != targetNode) {
                tmp = tmp.next;
            }
            tmp.next = null;//删除targetNode;
        } else {//目标节点是中间节点
            ListNode tmp = head;
            while(tmp.next != targetNode) {
                tmp = tmp.next;
            }
            tmp.next = tmp.next.next;//删除targetNode;
            targetNode = null;
        }
    }
}