HW6.20

 public class Solution
 {
     public static void main(String[] args)
     {
         int[][] chessboard = new int[8][8];

         while(true)
         {
             putQueens(chessboard);

             if(judgeCorrect(chessboard) == true)
             {
                 drawChessboard(chessboard);
                 break;
             }
             else
                 clearChessboard(chessboard);
         }
     }

     //put 8 queens on the chessboard randomly
     public static void putQueens(int[][] array)
     {
         int position;

         for(int i = 0; i < 8; i++)
         {
             position = (int)(Math.random() * 8);
             array[i][position] = 1;
         }
     }

     //clear the chessboard
     public static void clearChessboard(int[][] array)
     {
         for(int i = 0; i < 8; i++)
             for(int j = 0; j < 8; j++)
                 array[i][j] = 0;
     }

     //judge if there is only one chess in a row
     public static boolean judgeRow(int[][] array, int x, int y)
     {
         for(int i = y - 1; i >= 0; i--)
             if(array[x][i] == 1)
                 return false;
         for(int i = y + 1; i < 8; i++)
             if(array[x][i] == 1)
                 return false;
         return true;
     }

     //judge if there is only one chess in a column
     public static boolean judgeColumn(int[][] array, int x, int y)
     {
         for(int i = x - 1; i >= 0; i--)
             if(array[i][y] == 1)
                 return false;
         for(int i = x + 1; i < 8; i++)
             if(array[i][y] == 1)
                 return false;
         return true;
     }

     //judge if there is only one chess in the lean from left-top to right-bottom
     public static boolean judgeLeanTopToBottom(int[][] array, int x, int y)
     {
         for(int i = x - 1, j = y - 1; i >= 0 && j >= 0; i--, j--)
             if(array[i][j] == 1)
                 return false;
         for(int i = x + 1, j = y + 1; i < 8 && j < 8; i++, j++)
             if(array[i][j] == 1)
                 return false;
         return true;
     }

     //judge if there is only one chess in the lean from left-bottom to right-top
     public static boolean judgeLeanBottomToTop(int[][] array, int x, int y)
     {
         for(int i = x + 1, j = y - 1; i < 8 && j >= 0; i++, j--)
             if(array[i][j] == 1)
                 return false;
         for(int i = x - 1, j = y + 1; i >= 0 && j < 8; i--, j++)
             if(array[i][j] == 1)
                 return false;
         return true;
     }

     //judge if all the queens are put correctly
     public static boolean judgeCorrect(int[][] array)
     {
         int[] putX = new int[8];
         int[] putY = new int[8];

         for(int i = 0; i < 8; i++)
             for(int j = 0; j < 8; j++)
                 if(array[i][j] == 1)
                 {
                     putX[i] = i;
                     putY[i] = j;
                     break;
                 }

         for(int i = 0; i < 8; i++)
         {
             if(!(judgeRow(array, putX[i], putY[i]) && judgeColumn(array, putX[i], putY[i])
                 && judgeLeanTopToBottom(array, putX[i], putY[i]) && judgeLeanBottomToTop(array, putX[i], putY[i])))
                 return false;
         }
         return true;
     }

     public static void drawChessboard(int[][] array)
     {
         for(int i = 0; i < 8; i++)
         {
             for(int j = 0; j < 8; j++)
             {
                 if(array[i][j] == 1)
                     System.out.print("Q");
                 else
                     System.out.print("-");
             }
             System.out.println();
         }
     }
 }