The test case [3, 1, 3] is not valid because, as the description states, we are given an unsorted array containing n+1 numbers taken from the range 1 to n.

This implies that:

nums.length=n+1

In this case, 3=n+1, which means n=2. Therefore, the maximum number in this ...

I spent a hot minute before realizing this ha ha.

In the cycle detection solution, you don't have to actually get the cycle length. Just detect if there is a cycle then iterate through the pointers to check if they match