Solution to Connect 4 in GridWorld practice problem 3

Complete the Connect 4 in GridWorld practice problem before reviewing the solution.

Review the Connect 4 solution with AP CS Tutor Brandon Horn.

The method documentation from the original practice problem has been omitted.

public class BoardUtilities
{
  private BoundedGrid board;

  public BoardUtilities(BoundedGrid board)
  {
    this.board = board;
  }

  public int countDiscs(Location loc, boolean color, int dir)
  {
    Location nextLoc = loc.getAdjacentLocation(dir);

    if (!board.isValid(nextLoc) || board.get(nextLoc) == null
        || board.get(nextLoc).color() != color)
      return 0;

    return 1 + countDiscs(nextLoc, color, dir);
  }

  public int firstEmptyRow(int col)
  {
    Location firstEmptySpot = null;

    // find first empty spot in column from bottom
    for (int row = board.getNumRows() - 1; row >= 0 && firstEmptySpot == null; row--)
    {
      Location currentSpot = new Location(row, col);
      if (board.get(currentSpot) == null)
        firstEmptySpot = currentSpot;
    }

    return firstEmptySpot != null ? firstEmptySpot.getRow() : -1;
  }

  public boolean wouldWin(boolean color, int col)
  {
    return connectingDiscs(color, col) >= 4;
  }

  public int connectingDiscs(boolean color, int col)
  {
    int row = firstEmptyRow(col);

    if (row == -1) // column is full
      return 0;

    Location dropLocation = new Location(row, col);

    int maximumConnectingDiscs = 0;

    for (int direction = 0; direction <= 135; direction += 45)
    {
      int connectingDiscs = countDiscs(dropLocation, color, direction)
          + countDiscs(dropLocation, color, direction + Location.HALF_CIRCLE);
      if (connectingDiscs > maximumConnectingDiscs)
        maximumConnectingDiscs = connectingDiscs;
    }

    return maximumConnectingDiscs + 1;
  }

  public ArrayList validMoves()
  {
    ArrayList validMoves = new ArrayList();

    for (int col = 0; col < board.getNumCols(); col++)
      if (firstEmptyRow(col) != -1)
        validMoves.add(col);

    return validMoves;
  }

  public boolean turn()
  {
    int blueDiscs = 0;
    int redDiscs = 0;
    for (Location loc : board.getOccupiedLocations())
    {
      if (board.get(loc).color())
        blueDiscs++;
      else
        redDiscs++;
    }
    return blueDiscs == redDiscs;
  }
}