# DWITE Online Computer Programming Contest

## Forest Fires

December 2010
Problem 4

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 consume the entire forest.

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

• . – blank space
• T – a tree
• F – a tree on fire

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, each stating the time it takes for the fire to consume 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```