Flood Fill Logic Question

[luckielordie]

Hi there,
I am writing an agent that will play a game of Tron. This was one of the Google AI challenges.
I have been trying to use a Flood Fill to calculate the area I have to move my sprite. combined with the minimax algorithm I should be able to look out for areas that block my agent in.

However my flood fill always appears to be returning zero and I cant work out why. It's 5am here so I think it might be my logic, can someone check it for me? I'd love to see this thing running before I go to sleep.

int Board::FloodFill(int playerX, int playerY, vector<vector<int>>board)
{
	int area = 0;
	if(!isFree(playerX, playerY)) return area;
	board[playerY][playerX] = WALL;
	area++;

	area += FloodFill(playerX - 1, playerY, board); //west
	area += FloodFill(playerX + 1, playerY, board); //east
	area += FloodFill(playerX, playerY - 1, board); //north
	area += FloodFill(playerX, playerY + 1, board); //south

	return area;
}

bool isFree(int x, int y)
{
        return board[y][x] == EMPTY;		
}

[ne555]

Because you are passing `board' by value, the modifications are local to the function.
That means that `north' is not aware of all the cells that were visited by `west'.

In order to revert to original, either made a wrapper or `paint' with another colour.


> my flood fill always appears to be returning zero
Make a step-by-step run trough a debugger.
Probably the function is always stopping at `isFree()' because your starting cell has the player.