Given `head`, the head of a linked list, determine if the linked list has a cycle in it.

There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the `next` pointer. Internally, `pos` is used to denote the index of the node that tail’s `next` pointer is connected to. Note that `pos` is not passed as a parameter.

Return `true` if there is a cycle in the linked list. Otherwise, return `false`.

Example 1:

```Input: head = [3,2,0,-4], pos = 1
Output: true
Explanation: There is a cycle in the linked list, where the tail connects to the 1st node (0-indexed).
```

Example 2:

```Input: head = [1,2], pos = 0
Output: true
Explanation: There is a cycle in the linked list, where the tail connects to the 0th node.
```

Example 3:

```Input: head = [1], pos = -1
Output: false
Explanation: There is no cycle in the linked list.
```

Constraints:

• The number of the nodes in the list is in the range `[0, 104]`.
• `-105 <= Node.val <= 105`
• `pos` is `-1` or a valid index in the linked-list.

Can you solve it using `O(1)` (i.e. constant) memory?

Idea:

Use fast and slow pointers traversal, you they can meet each other then there is a circle

Solution:

``````/**
* function ListNode(val) {
*     this.val = val;
*     this.next = null;
* }
*/

/**
* @return {boolean}
*/