Fix free tile counting

Bug was giving percentage above 100% in exploring tile rates

main.cc

@@ -67,17 +67,15 @@ class World
 			// Add walls to the first and last columns
 			for (unsigned int i = 0; i < h; i++)
 			{
-				board[i * l] = WALL;
-				board[i * l + l - 1] = WALL;
-				tileQuantity -= 2;
+				markOne(i * l, WALL);
+				markOne(i * l + l - 1, WALL);
 			}
 
 			// Add walls to the first and last lines
 			for (unsigned int j = 0; j < l; j++)
 			{
-				board[j] = WALL;
-				board[(h - 1) * l + j] = WALL;
-				tileQuantity -= 2;
+				markOne(j, WALL);
+				markOne((h - 1) * l + j, WALL);
 			}
 
 			for (unsigned int i = 0; i < h; i++)
@@ -87,10 +85,7 @@ class World
 					// add a wall in this tile with probability p and provided that it is neither
 					// the starting tile nor the goal tile 
 					if ((double) rand() / RAND_MAX < p && !(i == 1 && j == 1) && !(i == h - 2 && j == l - 2))
-					{
-						board[i * l + j] = WALL;
-						tileQuantity --;
-					}
+						markOne(i * l + j, WALL);
 				}
 			}
 		}
@@ -188,6 +183,9 @@ class World
 
 		// Mark a point in the world
 		void markOne(unsigned int tile, int value = ORIGIN) {
+			if (value == WALL && board[tile] != WALL)
+				tileQuantity --;
+
 			board[tile] = value;
 		}