Linked List Cycle

Linked List Cycle

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

A cycle exists if some node in the list can be reached again by continuously following the next pointer. Internally, pos denotes the index of the node that the tail's next pointer is connected to (0-indexed). Note that pos is not passed as a parameter.

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

Examples

Example 1:

Input: head = [3, 2, 0, -4], pos = 1
Output: true
Explanation: There is a cycle 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 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 nodes in the list is in the range [0, 10^4].
• -10^5 <= Node.val <= 10^5
• pos is -1 or a valid index in the linked list.

Expected Complexity

• Time: O(n)
• Space: O(1)