Eight Queens Java algorithm

The eight Queens question, an old and famous problem, is a typical case of backtracking algorithms. The issue is the international chess player Max Bessel in 1848: Put eight queens on the 8x8 chess, so that they can not attack each other, that is, any two queens can not be in the same row, the same column or the same slash, ask how many kinds of pendulum

public class Queen{
private int [] column; //右上至左下是否有皇后 private int [] rup; //左上至右下是否有皇后 private int [] lup; private int [] queen; private int num; public Queen(){ column= new int [ 8 + 1 ]; rup= new int [( 2 * 8 )+ 1 ]; lup= new int [( 2 * 8 )+ 1 ]; for ( int i= 1 ;i<= 8 ;i++) column[i]= 0 ; for ( int i= 1 ;i<=( 2 * 8 );i++) rup[i]=lup[i]= 0 ;   //初始定义全部无皇后 queen= new int [ 8 + 1 ]; } public void backtrack( int i){ if (i> 8 ){ showAnswer(); } else { for ( int j= 1 ;j<= 8 ;j++){ if ((column[j]== 0 )&&(rup[i+j]== 0 )&&(lup[i-j+ 8 ]== 0 )){ //若无皇后 queen[i]=j; //设定为占用 column[j]=rup[i+j]=lup[i-j+ 8 ]= 1 ; backtrack(i+ 1 );   //循环调用 column[j]=rup[i+j]=lup[i-j+ 8 ]= 0 ; } } } } protected void showAnswer(){ num++; System.out.println( "\n解答" +num); for ( int y= 1 ;y<= 8 ;y++){ for ( int x= 1 ;x<= 8 ;x++){ if (queen[y]==x){ System.out.print( "Q" ); } else { System.out.print( "." ); } } System.out.println(); } } public static void main(String[]args){ Queen queen= new Queen(); queen.backtrack( 1 ); } }

Eight Queens Java algorithm