This problem is about finding a route on a square grid. The starting point is $(1,1)$ and the target point $(n,m)$. I can move each step from my current point $(x,y)$ either to $(x+y,y)$ or $(x,y+x)$. Now I need to determine if there is a path from $(1,1)$ to $(n,m)$, and if so to return the shortest one.
Now I believe that if I trace back my steps from the input point $(n,m)$ I can always know which move I made out of the two possible ones since if $n=m$ then there is no route, this means I'm always take the smaller coordinate and subtract it from the bigger one. But that means I have at most only one possible route to $(n,m)$ so why was I asked to return the shortest one?
Am I missing anything ?