判斷單鏈表是否有環

public class Link {
	static class Node
	{
		int val;
		Node next;
		public Node(int val)
		{
			this.val=val;
		}
	}


	static boolean isLinkedListContainsLoop(Node head){
		if(head==null){
			return false;
		}
		Node slowPtr=head;
		Node fastPtr=head;
		while(slowPtr.next!=null && fastPtr.next.next!=null){
			slowPtr=slowPtr.next;
			fastPtr=fastPtr.next.next;
			if(slowPtr==fastPtr){
				return true;
			}
		}
		return false;
	}


	public static void main(String[] args) {
		Node n1=new Node(1);
		Node n2=new Node(2);
		Node n3=new Node(3);
		Node n4=new Node(4);
		n1.next=n2;
		n2.next=n3;
		n3.next=n4;
		n4.next=n3;
		System.out.println(isLinkedListContainsLoop(n1));

	}

}

當fast按照每次2步，slow每次一步的方式走，發現fastPtr和slowPtr重合，確定了單向鏈表有環路。