It is possible that the faster one never steps foot on the slower one,
depending on the speeds of the two pointers, the length of the loop, the
starting distance of these two pointers inside the loop.
For example, if the slower one speed is one node per move and the faster
one is 3 node per move, the loop length is 2 and the starting distance is
1. Then they will never overlap.
You can get the formula having these four variables to decide whether the
two pointers can overlap, after how many loop