How do you find the number of the shortest distances between two points on a grid where you can only move one unit up, down, left, or right? Is there a formula for this?
Eg. The shortest path between $(0,0)$ and $(1,1)$ can be $(0,0)\to (0,1)\to (1,1)$ or $(0,0)\to(1,0)\to(1,1)$, so there are two shortest paths.