Java实现单链表，反转链表，检测是否成环

**Java 实现单链表**

### 链表定义

javapublic class Node {
 int data;
 Node next;

 public Node(int data) {
 this.data = data;
 this.next = null;
 }
}

javapublic class LinkedList {
 private Node head;

 public void addNode(int data) {
 Node newNode = new Node(data);
 if (head == null) {
 head = newNode;
 } else {
 Node temp = head;
 while (temp.next != null) {
 temp = temp.next;
 }
 temp.next = newNode;
 }
 }

 public void printList() {
 Node temp = head;
 while (temp != null) {
 System.out.print(temp.data + " ");
 temp = temp.next;
 }
 System.out.println();
 }
}

javapublic class LinkedList {
 // ...

 public void reverseList() {
 Node prev = null;
 Node current = head;
 while (current != null) {
 Node nextNode = current.next;
 current.next = prev;
 prev = current;
 current = nextNode;
 }
 head = prev;
 }

 public void printReverseList() {
 reverseList();
 Node temp = head;
 while (temp != null) {
 System.out.print(temp.data + " ");
 temp = temp.next;
 }
 System.out.println();
 // 回复链表 reverseList();
 }
}

javapublic class LinkedList {
 // ...

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

 public void printCycle() {
 if (!hasCycle()) {
 System.out.println("No cycle found.");
 return;
 }
 Node slow = head;
 Node fast = head;
 while (fast != null && fast.next != null) {
 slow = slow.next;
 fast = fast.next.next;
 if (slow == fast) {
 break;
 }
 }
 System.out.println("Cycle detected at node " + slow.data);
 }
}

javapublic class Main {
 public static void main(String[] args) {
 LinkedList list = new LinkedList();
 list.addNode(1);
 list.addNode(2);
 list.addNode(3);
 list.addNode(4);
 list.addNode(5);

 System.out.println("Original List:");
 list.printList();

 System.out.println("Reversed List:");
 list.reverseList();
 list.printList();

 System.out.println("Has Cycle: " + list.hasCycle());

 System.out.println("Print Cycle:");
 list.printCycle();
 }
}