八皇后

public class huanghou {

        private int[] column;//同栏是否有皇后，1表示有
        private int[] rup;//右上至左下是否有皇后
        private int[] lup;//左上至右下是否有皇后
        private int[] queen;//解答
        private static int num;//解答编号
        public huanghou() {
            column = new int[8+1];
            rup  = new int[2*8];
            lup  = new int[2*8];
            for (int i = 1; i <= 8; i++) {
                column[i] = 0;
            }
            for (int i = 1; i <= 8; i++) {
                rup[i] = lup[i] = 0;
            }
            queen = new int[8+1];
        }
        
        private void backtrack(int i) {
            if(i>8) {
                num++;
                showAnswer();
            }else {
                for (int j = 1; j <= 8; j++) {
                    if((column[j] == 0)&&(rup[i+j-1] == 0)&&(lup[i-j+8] == 0)) {
                        queen[i] = j;//放置第i个皇后
                        column[j] = rup[i+j-1] = lup[i-j+8] = 1;//同栏，同斜线上不能再放置皇后
                        backtrack(i+1);//准备放置第i+1个皇后
                        column[j] = rup[i+j-1] = lup[i-j+8] = 0;//撤回第i个皇后
                    }
                }
            }
        }
        
//        输出所有情况
        protected void showAnswer() {
            System.out.println("\n解答" + num);
            
            for (int i = 1; i <= 8; i++) {
                for (int j = 1; j <= 8; j++) {
                    if (queen[i] == j) {
                        System.out.print("Q");
                    }else {
                        System.out.print(".");
                    }
                }
                System.out.println();
            }
        }

        public static void main(String[] args) {
            huanghou h=new huanghou();
            h.backtrack(1);
            System.out.println(num);//输出最终种类数
        }

}