第一次实验，8皇后问题算法

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public class EightQueen {     Queen[] stack = new Queen[8];    int sp = 0;    int num = 0;     public EightQueen() {      num = 8;      stack = new Queen[num];      sp = 0;    }     public EightQueen(int num) {      this.num = num;      stack = new Queen[num];      sp = 0;    }     /*打印皇后的坐标列表。*/    public void list() {      System.out.println("开始列表中堆栈指针以及8皇后问题的解:");      for (int i = 0; i < sp; i++) {       stack[i].pos.println();      }      System.out.println("结束列表堆栈指针:");    }     /*主算法流程。@Administrator**/    public void calc() {      sp = 0;      stack[sp++] = new Queen();      while (sp >= 0 && sp <= num - 1) {       Queen queen = getQueen(sp);       if (null == queen) {        boolean flag = true;        while (flag) {         --sp;         if (sp < 0)          break;         if (stack[sp].pos.y == num - 1) {          }         else {          stack[sp++].pos.y++;          flag = false;          for (int k = 0; k < sp - 1; k++) {           if (stack[k].isUnderControl(stack[sp - 1].pos)) {            flag = true;            break;           }          }         }        }        }       else {        stack[sp++] = queen;       }      }     }     public Queen getQueen(int x) {      boolean flag = true;      int y = 0;      while (flag) {       flag = false;       for (int i = 0; i < x; i++) {        if (stack[i].isUnderControl(new Point(x, y))) {         flag = true;         break;        }       }       if (flag && y <= num - 1) {        y++;       }       else if (y >= num) {        return null;       }      }      return new Queen(new Point(x, y));    }     public static void main(String[] args) {      EightQueen a = new EightQueen(20);      a.calc();      if (a.sp > 0) {       a.list();      }      else {       System.out.println("这个问题无解！");      }    }    }     class Point {    int x, y;     public void println() {      System.out.println("指针是 ：[x,y]=[" + x + "," + y + "]");    }     public Point() {      x = 0;      y = 0;    }     public Point(int x, int y) {      this.x = x;      this.y = y;    }    /**      * @return int      */    public int getX() {      return x;    }     /**      * @return int      */    public int getY() {      return y;    }     /**      * 设置 x.      * @param x The x to set      */    public void setX(int x) {      this.x = x;    }     /**      * 设置 y.      * @param y The y to set      */    public void setY(int y) {      this.y = y;    }    }     class Queen {    Point pos;    public Queen() {      pos = new Point();    }    public Queen(Point pos) {      this.pos = pos;    }    public boolean isUnderControl(Point point) {      boolean ret = true;      if (point.x != pos.x       && point.y != pos.y       && Math.abs(point.x - pos.x) != Math.abs(point.y - pos.y)       && Math.abs(point.x + point.y) != Math.abs(pos.x + pos.y)) {       ret = false;      }      return ret;    }    }
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