环形链表
出处
leetcode｜环形链表
题解/思路
快慢指针
- 空间复杂度 O(1)
- 时间复杂度 O(n)
快指针比慢指针跨度大
- 快指针遍历结束，说明没有环
- 快指针和慢指针相等，说明有环
```
/**
- Definition for singly-linked list.
- function ListNode(val) {
- this.val = val;
- this.next = null;
- }
*/
/**
- @param {ListNode} head
- @return {boolean}
*/
var hasCycle = function(head) {
if (!head || !head.next) return false;
let slow = head;
let fast = head.next;
while (fast !== slow) {
// fast节点遍历结束
if (!fast || !fast.next) {
return false
}
fast = fast.next.next;
slow = slow.next;
}
return true;
};
```