数据结构与算法-找到环的入口

package linkedlist;

public class LinkedList {

	public static Node isCycle(Node head){
		Node p1 = head;
		Node p2 = head;
		while (p2 != null && p2.next != null){
			p1 = p1.next;
			p2 = p2.next.next;
			if (p1 == p2){
				Node index1 = p2;
                Node index2 = head;
                while (index1 != index2) {
                    index1 = index1->next;
                    index2 = index2->next;
                }
                return index2; // 返回环的入口
			}
		}
		return null;
	}
	public static void main(String[] args) {
		Node node1 = new Node(5);
		Node node2 = new Node(3);
		Node node3 = new Node(7);
		Node node4 = new Node(2);
		Node node5 = new Node(6);
		node1.next = node2;
		node2.next = node3;
		node3.next = node4;
		node4.next = node5;
		node5.next = node1;
		System.out.println(isCycle(node1));
	}

	private static class Node{
		int data;
		Node next = null;
		Node(int data){
			this.data = data;
		}
	}
}