nvm

This can be kind of wasteful because it is computing all possible paths, including the ones which may never be required for a particular problem. It's fine on small problem sets, but consider a big grid where your destination is the first column, last row. You could arrive at the answer by just traversing down, but this solution would cover the entire grid first.

The use of reduce seems superfluous when you can simply new Set([1,2,3,...]);