141.环形链表 /* * @lc app=leetcode.cn id=141 lang=typescript * * [141] 环形链表 */ // @lc code=start /** * Definition for singly-linked list. * class ListNode { * val: number * next: ListNode | null * constructor(val?: number, next?: ListNode | null) { * this.val = (val===undefined ? 0 : val) * this.next = (next===undefined ? null : next) * } * } */ function hasCycle(head: ListNode | null): boolean { if (head === null || head.next === null) return false; let slow = head; let fast = head.next; while (slow !== fast) { if (fast === null || fast.next === null) return false; slow = slow.next; fast = fast.next.next; } return true; } // @lc code=end