Check Cycle
给定一个链表,判断它是否有环。
样例
给出 -21->10->4->5, tail connects to node index 1,返回 true
挑战
不要使用额外的空间
Solution
快慢指针
Complexity
时间复杂度 O(n),空间复杂度 O(1)
Code
/**
* Definition for ListNode.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int val) {
* this.val = val;
* this.next = null;
* }
* }
*/
public class Solution {
/**
* @param head: The first node of linked list.
* @return: True if it has a cycle, or false
*/
public boolean hasCycle(ListNode head) {
if(head == null)
return false;
ListNode fast = head;
ListNode slow = head;
while(fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
if(slow == fast)
return true;
}
return false;
}
}