/*
 * Complete the 'bomberMan' function below.
 *
 * The function is expected to return a STRING_ARRAY.
 * The function accepts following parameters:
 *  1. INTEGER n
 *  2. STRING_ARRAY grid
 */
public static List<String> bomberMan(int n, List<String> grid) {
	if (n == 0 || n == 1) {
		return grid;
	}
	// 3 -> 7 -> 11 -> 15 ...
	if (n == 3 || ((n - 4) % 4) == 3) {
		return bombsDetonateState3(grid);
	}
	// 5 -> 9 -> 13 ..
	if (((n - 4) % 4) == 1) {
		return bombsDetonateState5(grid);
	}
	if (n % 2 == 0) {
		return boardFullOfBombsState(grid);
	}
	return grid;
}

private static List<String> bombsDetonateState3(List<String> grid) {
	return explodeBombs(grid);
}

private static List<String> bombsDetonateState5(List<String> grid) {
	List<String> baseGrid = bombsDetonateState3(grid);
	return explodeBombs(baseGrid);
}

private static List<String> explodeBombs(List<String> grid) {
	List<String> newGrid = new ArrayList<>();
	for (int i = 0; i < grid.size(); i++) {
		StringBuilder sb = new StringBuilder();
		for (int j = 0; j < grid.get(0).length(); j++) {
			char current = grid.get(i).charAt(j);
			char up = i - 1 >= 0 ? grid.get(i - 1).charAt(j) : '.';
			char down = i + 1 < grid.size() ? grid.get(i + 1).charAt(j) : '.';
			char left = j - 1 >= 0 ? grid.get(i).charAt(j - 1) : '.';
			char right = j + 1 < grid.get(0).length() ? grid.get(i).charAt(j + 1) : '.';
			if (current == 'O') {
				sb.append('.');
			} else if (up == 'O' || down == 'O' || left == 'O' || right == 'O') {
				sb.append('.');
			} else {
				sb.append('O');
			}
		}
		newGrid.add(sb.toString());
	}
	return newGrid;
}

private static List<String> boardFullOfBombsState(List<String> grid) {
	return grid.stream().map(s -> "O".repeat(grid.get(0).length())).collect(toList());
}