Java实现单链表，反转链表，检测是否成环

class ListNode {
    int val;
    ListNode next;
    
    public ListNode(int val) {
        this.val = val;
        this.next = null;
    }
}

class LinkedList {
    ListNode head;
    
    public LinkedList() {
        this.head = null;
    }
    
    // 向链表末尾添加节点
    public void addNode(int val) {
        ListNode newNode = new ListNode(val);
        
        if (head == null) {
            head = newNode;
        } else {
            ListNode current = head;
            while (current.next != null) {
                current = current.next;
            }
            current.next = newNode;
        }
    }
    
    // 反转链表
    public void reverseList() {
        ListNode prev = null;
        ListNode current = head;
        
        while (current != null) {
            ListNode nextNode = current.next;
            current.next = prev;
            prev = current;
            current = nextNode;
        }
        
        head = prev;
    }
    
    // 检测链表是否成环
    public boolean hasCycle() {
        if (head == null)
            return false;
        
        ListNode slow = head;
        ListNode fast = head.next;
        
        while (fast != null && fast.next != null) {
            if (slow == fast)
                return true;
            
            slow = slow.next;
            fast = fast.next.next;
        }
        
        return false;
    }
}

测试用例

public class Main {
    public static void main(String[] args) {
        LinkedList linkedList = new LinkedList();
        linkedList.addNode(1);
        linkedList.addNode(2);
        linkedList.addNode(3);
        
        // 反转链表
        linkedList.reverseList();
        
        // 检测链表是否成环
        System.out.println(linkedList.hasCycle());
    }
}