Java语言 检测单链表是否有环

 

/**
* 判断链表是否有环
* @author Administrator
*
*/
public class P238 {
public static void main(String[] args) {
Scanner in=new Scanner(System.in);
char[] c=in.nextLine().toCharArray();
in.close();
SystemIn inn=new SystemIn();
Node1 head=inn.systemIn(c);
Node1 h=head;
inn.systemOut(h);
System.out.print(IsLoop(head));

}
public static Node1 systemIn(char[] ch) {
if(ch==null||ch.length==0) return null;
Node1 head=new Node1('0');
Node1 temp=head;
for(int i=0;i<ch.length-1;i++) {
Node1 cur=new Node1(ch[i]);
temp.next=cur;
temp=temp.next;
}
return head.next;
}
public static boolean IsLoop(Node1 head) {
Node1 low =head;
Node1 fast=head;
if(fast==null) return false;
while(fast!=null&&fast.next!=null&&fast.next.next!=null) {
low=low.next;
fast=fast.next.next;
if(low==fast) {
return true;
}
}
return !(fast==null||fast.next==null);
}

}