detect circle in linked list

Question

A Singly Linked List is a bunch of nodes linked in one direction.

class Node {
  val: any
  next: Node
  constructor(val: any, next:Node) {
    this.val = val
    this.next = next
  }
}

const node2 = new Node(2)
const node1 = new Node(1, node2) // connect 1 -> 2

A Node might link to a node before it, thus creating a circle.

Can you write a function to detect it?

Follow-up

What is the space cost for your approach? Can you solve it without extra space?

Code

/**
 * @param {Node} head
 * @return {boolean}
 */
function hasCircle(head) {
  // your code here
}

Source

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