Linked List Cycle

Linked List Cycle

问题：

Given a linked list, determine if it has a cycle in it.

思路：

快指针，慢指针方法

我的代码：

public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head == null || head.next == null)
            return false ;
        ListNode one = head ;
        ListNode two = head.next.next ;
        while(one != null && two != null)
        {
            if(one == two)
                return true ;
            one = one.next ;
            if(two.next == null)
                break ;
            two = two.next.next ;
        }
        return false ;
        
    }
}

他人代码：

public class Solution {
    public boolean hasCycle(ListNode head) {
        if (head == null) {
            return false;
        }

        ListNode fast = head, slow = head;
        do {
            if (fast.next == null || fast.next.next == null) {
                return false;
            }
            fast = fast.next.next;
            slow = slow.next;
        } while (fast != slow);

        return true;
    }
}

学习之处：

• 如果没有cycle，快指针肯定先到null
• do while的妙用 可以进行一次判断了

 

if(null==node || node.next==null) return false;

ListNode slowNode = node;
ListNode fastNode = node.next.next;

while(fastNode!=null && fastNode.next!=null){
if(slowNode == fastNode) return true;
slowNode = slowNode.next;
fastNode = fastNode.next.next;
}

return false;