Career cup 9.9

EightQueen.java

package Chapter9;

import java.util.ArrayList;

public class EightQueen {
    public static final int CHESS_BOARD_LENGTH = 8;
    public static int count = 0;
    
    //Check if the position is valid based on previous assignment of other queens
    private static boolean isValid(int row, int col, ArrayList<Integer> prevRows) {
	for(int i = 0; i < col; i++) {
	    if(row == prevRows.get(i) || Math.abs(row - prevRows.get(i)) == col - i)
		return false;
	}
	return true;
    }
    
    public static void printAll() {
	count = 0;
	printAllWays(0, new ArrayList<Integer>());
    }
    
    private static void printAllWays(int curCol, ArrayList<Integer> prevRows) {
	for(int row = 0; row < CHESS_BOARD_LENGTH; row++) {
	    if(!isValid(row, curCol, prevRows))
		continue;
	    
	    int nextCol = curCol + 1;
	    ArrayList<Integer> nextRows = new ArrayList<Integer>();
	    nextRows.addAll(prevRows);
	    nextRows.add(row);
	    if(nextCol == CHESS_BOARD_LENGTH)
		printBoard(nextRows);
	    else {
		printAllWays(nextCol, nextRows);
	    }
	}
    }

    //print the chess board for testing
    private static void printBoard(ArrayList<Integer> nextRows) {
	System.out.println("Chess Board " + (count++) + ": ");
	for(int row = 0; row < CHESS_BOARD_LENGTH; row++) {
	    for(int col = 0; col < CHESS_BOARD_LENGTH; col++) {
		if(nextRows.get(col) == row)
		    System.out.print(". ");
		else
		    System.out.print("X ");
	    }
	    System.out.println();
	}
	System.out.println();
    }
    
    public static void main(String[] args) {
	EightQueen.printAll();
    }
}