Problem: 141. 环形链表

思路

👨‍🏫 参考题解

💖 快慢指针法

时间复杂度: $O(n)$
空间复杂度: $O(1)$

/*** Definition for singly-linked list.* class ListNode {*     int val;*     ListNode next;*     ListNode(int x) {*         val = x;*         next = null;*     }* }*/
public class Solution {public boolean hasCycle(ListNode head){int cnt = 0;ListNode slow = head;ListNode fast = head;while (fast != null){fast = fast.next;if (fast != null)fast = fast.next;if (fast == slow)return true;slow = slow.next;}return false;}
}

💖 计步器法

时间复杂度: $O(n)$
空间复杂度: $O(1)$

/*** Definition for singly-linked list.* class ListNode {*     int val;*     ListNode next;*     ListNode(int x) {*         val = x;*         next = null;*     }* }*/
public class Solution {public boolean hasCycle(ListNode head){if(head == null)return false;int cnt = 0;while (cnt < 10000){cnt++;if (head.next == null)return false;head = head.next;}return true;}
}