package 链表;

/**
 * https://leetcode-cn.com/problems/delete-node-in-a-linked-list/
 * @author MJ Lee
 *
 */
public class _237_删除链表中的节点 {
    
    public void deleteNode(ListNode node) {
        node.val = node.next.val;
        node.next = node.next.next;
    }
}

    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) return head;
    
        ListNode newHead = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return newHead;
    }

public ListNode reverseList2(ListNode head) {
        if (head == null || head.next == null) return head;
    
        ListNode newHead = null;
        while (head != null) {
            //tmp的作用临时变了 保存变量值 防止节点引用断裂 从而被gc误删
            ListNode tmp = head.next;
            head.next = newHead;
            newHead = head;
            head = tmp;
        }
        
        return newHead;
    }

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