打印输出蛇形矩阵

package job;

public class snake {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int n = 5;
		int x=0, y= n-1;
		int tot=1;
		
		int[][] a = new int[n][n];
		for(int i=0;i<n;i++)
			for(int j=0;j<n;j++)
				a[i][j]=0;
		a[0][n-1]=1;		
		while(tot<n*n) 
		{
			while((x+1<n)&&(a[x+1][y]==0)) {++x; ++tot; a[x][y]=tot;}
			while((y-1>=0)&&(a[x][y-1]==0)) {--y; ++tot; a[x][y]=tot;}
			while((x-1>=0)&&(a[x-1][y]==0)) {--x; ++tot; a[x][y]=tot;}
			while((y+1<n)&&(a[x][y+1]==0)) {++y; ++tot; a[x][y]=tot;}
		}
		
		for(int i=0;i<n;i++)
		{
			for(int j=0;j<n;j++)
			{
				System.out.format("%4d", a[i][j]);
			}
			System.out.println();
		}
		
	}

}

  13  14  15  16   1
  12  23  24  17   2
  11  22  25  18   3
  10  21  20  19   4
   9   8   7   6   5