Length of the Cycle

Return the number of nodes in the cycle, or 0 if the list has no cycle.

A list can have a cycle: the last node's next points back at an earlier node. The tests give such a list as {"values": [...], "cycle": k}, where the last node points back at node k (counting from 0), and k = -1 means no cycle.

Examples

Example 1

Input:

cycle_length(head)  # head = 3 -> 2 -> 0 -> -4, and -4 points back at 2

Output:

3

Example 2

Input:

cycle_length(head)  # head = 1 -> 2, no cycle

Output:

0

Constraints

• 0 <= number of nodes <= 100000
• The cycle position k is -1 or a valid index.