UVa 10977 - Enchanted Forest

Summary
Find length of the shortest path between two points on a 2D grid. Some of grid points may be blocked.

Explanation
It's another straightforward shortest path problem. BFS is the classical algorithm here.

Gotchas

 * When there's no path print "Impossible." (without the quotes, but with the dot.)
 * Jigglypuff at location $$(R,C)$$ having loudness $$L$$ blocks all grid points $$(r,c)$$ satisfying: $$(R-r)^2+(C-c)^2 \le L^2$$. Using this inequality you can get rid of floating-point variables.

Input
5 5 5 1 2 1 3 1 4 1 5 2 5 1 4 3 1 0 0

Output
8