//将对应的链表逆置
    public ListNode reverse(ListNode head){
        ListNode prev=null;
        ListNode p=head;
        while(p!=null){
            //保存对应的结点指针
            ListNode temp=p.next;
            //连接
            p.next=prev;
            prev=p;
            p=temp;
        }
        return prev;
    }

    //通过快慢指针找到中间节点
    public ListNode getMidListNode(ListNode head){
        //对于快慢指针
        ListNode slow=head;
        ListNode fast=head;
        while(fast.next!=null&&fast.next.next!=null){//
            slow=slow.next;
            fast=fast.next.next;
        }
        return slow;
    }

如果是要删除中间节点

需要找到中间节点的前一个结点，快慢结点指针同时从虚拟头节点开始出发即可

class Solution {
    public ListNode deleteMiddle(ListNode head) {
        ListNode dummy=new ListNode(0,head);
        ListNode slow=dummy;
        ListNode fast=dummy;
        while(fast.next!=null&&fast.next.next!=null){
            slow=slow.next;
            fast=fast.next.next;
        }
        slow.next=slow.next.next;
        return dummy.next;
    }
}

通过快慢指针判断是否有环

快慢指针判断是否有环

public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head==null||head.next==null){
            return false;
        }
        ListNode slow=head;
        ListNode fast=head.next;
        while(slow!=fast){
            if(fast==null||fast.next==null){
                return false;
            }
            slow=slow.next;
            fast=fast.next.next;
        }
        return true;
    }
}

环形链表入环节点

环形链表入环节点

public class Solution {
    public ListNode detectCycle(ListNode head) {
        if(head==null||head.next==null){
            return null;
        }
        ListNode slow=head;
        ListNode fast=head.next;
        while(slow!=fast){
            if(fast==null||fast.next==null){
                return null;
            }
            slow=slow.next;
            fast=fast.next.next;
        }

        ListNode ptr=head;
        slow=slow.next;//由于初始时候对应的起点已经先走一步了，所以将fast=head时候将slow=slow.next
        //如果对应的起点  slow=head;fast=head   对应的直接省略
        while(slow!=ptr){
            slow=slow.next;
            ptr=ptr.next;
        }
        return ptr;
    }
}