DWITE Online Computer Programming Contest
February 2012
Problem 4
Forest Fires

Forest fires are really dangerous, and can be started by even the smallest flame. Spreading from tree to tree, fires can engulf an entire forest in a matter of weeks. Given a map of a forest with locations of where a fire (or multiple fires) might have started, determine how long it would take the fire to capture the entire forest.

The input file DATA4.txt will contain 5 test cases, each a 10x10 map, followed by a line of 10 dashes for visual separation.

Fires only spread from existing fire to adjacent trees, in 4 directions (so not diagonally). It takes 1 unit of time for the fire to spread from one location to the next. The fire spreads in all 4 directions at the same time.

The output file OUT4.txt will contain 5 lines, the time it takes for the fire to capture the entire forest. If some piece of the forest survives, output -1.

Sample Input (first 2 shown):
..........
..........
..........
..........
..TTTTT...
..F...F...
..........
..........
..........
..........
----------
..........
..........
..........
...TT.TT..
...F......
..........
..........
..........
..........
..........
----------
		        
Sample Output (first 2 shown):
3
-1