placeQueens()次のコードでは、 への再帰呼び出しの数とへの呼び出しの数を計算できるようにしたいと考えていますisUnderAttack()。int counter = 0placeQueens() の最初の行に追加して、その後インクリメントしようとしましたqueenPlaced = placeQueens(column+1);が、奇妙な数字が表示され続けます。これを達成する方法はありますか？私のコードはどのくらい効率的ですか?
これは出力です：
1 0 0 0 0 0 0 0
0 0 0 0 0 0 1 0
0 0 0 0 1 0 0 0
0 0 0 0 0 0 0 1
0 1 0 0 0 0 0 0
0 0 0 1 0 0 0 0
0 0 0 0 0 1 0 0
0 0 1 0 0 0 0 0
Queen PLACED in [3][7]
Queen Placed: 1
Queen Placed: 1
Queen Placed: 1
Queen Placed: 1
Queen Placed: 2
Queen Placed: 3
Queen Placed: 3
Queen Placed: 1
私がこれを行うときplaceQueens()
if (!isUnderAttack(row, column))
{
setQueen(row, column); //consider next square in column
queenPlaced = placeQueens(column+1);
counter++;
System.out.println("Queen Placed: "+counter);
//if no queen is possible in next column,
.
public class Queens
{
//squares per row or column
public static final int BOARD_SIZE = 8;
//used to indicate an empty square
public static final int EMPTY = 0;
//used to indicate square contains a queen
public static final int QUEEN = 1;
private int board[][]; //chess board
//public int queens=0;
public Queens()
{
//constructor: Creates an empty square board.
board = new int[BOARD_SIZE][BOARD_SIZE];
for (int row = 0; row < BOARD_SIZE; row++)
{
for (int column = 0; column < BOARD_SIZE; column++)
{
board[row][column] = EMPTY;
}
}
}
//clears the board
//Precondition: None
//Postcondition: Sets all squares to EMPTY
public void clearBoard()
{
//loops through the rows
for(int row = 0; row < BOARD_SIZE; row++)
{
//loops through the columns
for (int column = 0; column < BOARD_SIZE; column++)
{
board[row][column] = EMPTY;
}
}
}
//Displays the board
//precondition: None
//postcondition: Board is written to standard output;
//zero is an EMPTY square, one is a square containing a queen (QUEEN).
public void displayBoard()
{
//int counter = 0;
for (int row = 0; row < BOARD_SIZE; row++)
{
System.out.println("");
for (int column = 0; column < BOARD_SIZE; column++)
{
System.out.print(board[row][column] + " ");
//if (board[row][column] == QUEEN)
//{
// counter++;
//}
}
}
System.out.println();
//System.out.println("Number of Recursive Calls to placeQueens: " + counter);
}
//Places queens in columns of the board beginning at the column specified.
//Precondition: Queens are placed correctly in columns 1 through column-1.
//Postcondition: If a solution is found, each column of the board contains one queen and
//method returns true; otherwise, returns false (no solution exists for a queen anywhere in column specified).
public boolean placeQueens(int column)
{
if(column >= BOARD_SIZE)
{
return true; //base case
}
else
{
boolean queenPlaced = false;
int row = 0; // number of square in column
int queensRemoved = 0;
while( !queenPlaced && (row < BOARD_SIZE))
{
//if square can be attacked
if (!isUnderAttack(row, column))
{
setQueen(row, column); //consider next square in column
queenPlaced = placeQueens(column+1);
//if no queen is possible in next column,
if(!queenPlaced)
{
//backtrack: remover queen placed earlier
//and try next square in column
removeQueen(row, column);
queensRemoved ++ ;
System.out.println("Queen Removed: "+queensRemoved);
//++row;
}
}
++row;
}
return queenPlaced;
}
}
//Sets a queen at square indicated by row and column
//Precondition: None
//Postcondition: Sets the square on the board in a given row and column to Queen.
private void setQueen(int row, int column)
{
board[row][column] = QUEEN;
displayBoard();
System.out.printf("Queen PLACED in [%d][%d]\n", row, column);
}
//removes a queen at square indicated by row and column
//Precondition: None
//Postcondition: Sets the square on the board in a given row and column to EMPTY.
private void removeQueen(int row, int column)
{
board[row][column] = EMPTY;
displayBoard();
System.out.printf("Queen REMOVED from [%d][%d]\n", row, column);
}
//Determines whether the square on the board at a given row and column is
//under attack by any queens in the columns 1 through column-1.
//Precondition: Each column between 1 and column-1 has a queen paced in a square at
//a specific row. None of these queens can be attacked by any other queen.
//Postcondition: If the designated square is under attack, returns true: otherwise return false.
private boolean isUnderAttack(int row, int column)
{
for (int y = 0; y < BOARD_SIZE; y++)
{
int x1 = row - column + y;
int x2 = row + column - y;
if (board[row][y] == QUEEN) //possible horizontal attack
return true;
if (0 <= x1 && x1 < BOARD_SIZE && board[x1][y] == QUEEN) //diagonal NW
return true;
if (0 <= x2 && x2 < BOARD_SIZE && board[x2][y] == QUEEN) //diagonal SW
return true;
}
return false;
}
private int index(int number)
{
//Returns the array index that corresponds to a row or column number.
//Precondition: 1 <= number <= BOARD_SIZE.
//Postcondition: Returns adjusted index value
return number -1 ;
}
//main to test program
public static void main(String[] args)
{
Queens Q = new Queens();
if(Q.placeQueens(0))
{
//Q.displayBoard();
}
else
{
System.out.println("Not Possible");
}
}
}