VL-Programmieren/VL05/Aufgabe02/Aufgabe02.java

package VL05.Aufgabe02;

/**
 * Vorlesung 5 / Aufgabe 2
 *
 * @author Sebastian Brosch
 */
public class Aufgabe02 {
  public static void main(String[] args) {
    final int DAMEN = 8;
    int chessboard[][] = new int[DAMEN][DAMEN];
    queens(chessboard, 1);
  }

  /**
   * Method to place a queen on the chessboard.
   *
   * @param chessboard The chessboard to place the queen.
   * @param q          The number of the queen to be placed.
   */
  private static void queens(int[][] chessboard, int q) {
    if (q > chessboard.length) {
      print(chessboard);
      return;
    } else {
      for (int i = 0; i < chessboard.length; i++) {
        if (isQueenPossible(chessboard, q - 1, i)) {

          chessboard[q - 1][i] = 1;
          queens(chessboard, q + 1);
          chessboard[q - 1][i] = 0;
        }
      }
    }
  }

  /**
   * Method to check whether a queen can be placed on the field.
   *
   * @param chessboard The chessboard to place the queen.
   * @param row        The row to place the queen.
   * @param column     The column to place the queen.
   * @return The state whether the queen can be placed on the field.
   */
  private static boolean isQueenPossible(int[][] chessboard, int row, int column) {
    int currentRow = 0;
    int currentColumn = 0;

    // check whether the queen can be placed in current row.
    for (int c = 0; c < chessboard[row].length; c++) {
      if (chessboard[row][c] == 1)
        return false;
    }

    // check whether the queen can be placed in current column.
    for (int r = 0; r < chessboard.length; r++) {
      if (chessboard[r][column] == 1)
        return false;
    }

    // check whether the queen can be placed diagonal (top left).
    currentRow = row;
    currentColumn = column;

    while (currentColumn >= 0 && currentRow >= 0) {
      if (chessboard[currentRow][currentColumn] == 1)
        return false;

      currentRow--;
      currentColumn--;
    }

    // check whether the queen can be placed diagonal (bottom right).
    currentRow = row;
    currentColumn = column;

    while (currentColumn < chessboard[row].length && currentRow < chessboard.length) {
      if (chessboard[currentRow][currentColumn] == 1)
        return false;

      currentRow++;
      currentColumn++;
    }

    // check whether the queen can be placed diagonal (bottom left).
    currentRow = row;
    currentColumn = column;

    while (currentColumn >= 0 && currentRow < chessboard.length) {
      if (chessboard[currentRow][currentColumn] == 1)
        return false;

      currentRow++;
      currentColumn--;
    }

    // check whether the queen can be placed diagonal (top right).
    currentRow = row;
    currentColumn = column;

    while (currentColumn < chessboard[row].length && currentRow >= 0) {
      if (chessboard[currentRow][currentColumn] == 1)
        return false;

      currentRow--;
      currentColumn++;
    }

    return true;
  }

  /**
   * Method to print a chessboard.
   *
   * @param chessboard The chessboard to be printed.
   */
  private static void print(int[][] chessboard) {
    System.out.println("\nChessboard:\n");

    for (int r = 0; r < chessboard.length; r++) {
      for (int c = 0; c < chessboard[r].length; c++) {
        System.out.printf("%d", chessboard[r][c]);
      }

      System.out.printf("\n");
    }
  }
}