打印螺旋矩阵2

public class Untitled {
     public static void main(String[] args) {

         final int N = 9;
         int[][] a = new int[N][N];

         int x = -1; int y = 0;
         int dx = 0; int dy = -1;

         int k = 1;
         while (true) {
             // rotate direction
             if (dx == 0 && dy == -1) { dx = 1; dy = 0; }
             else if (dx == 1 && dy == 0) { dx = 0; dy = 1; }
             else if (dx == 0 && dy == 1) { dx = -1; dy = 0; }
             else { dx = 0; dy = -1; }

             // move 1 step
             x += dx; y+= dy;

             if (a[x][y] != 0) { break; }
             else { a[x][y] = k++;}

             // move more steps
             while(true) {
                 int nx = x + dx; int ny = y + dy;
                 if (nx < 0 || nx >= N || ny < 0 || ny >= N) { break; }
                 if (a[nx][ny] != 0) { break; }
                 x = nx; y = ny;
                 a[x][y] = k++;
             }
         }

         for (int i = 0; i < N; i ++)  {
             for (int j = 0; j < N; j++) {
                 System.out.print(String.format("%3d", a[i][j]));
                 System.out.print(' ');
             }
             System.out.println();
         }
     }
 }