Queries regarding floyd's cycle

Below is the code for floyds cycle, I am not able to understand how to give input for the floyd cycle and how break the chain by making the prev pointer NULL, below is the code that I tried-

To give input, you have to form a circular linked list.
Refer this

Yeah I saw this one, but I want the ans through the concept that was explained in the video using fast and slow pointer, I want you to provide improvisation in the code that I have written and get ans using that.

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