解题思路： 

     int [][] arr = new int[n][m];
     int i = 0, j = -1, temp = 1;
     while (n * m > 0)
     {
            for (int p = 0; p < m; p++)//从左自右
                arr[i][j=j+1] = temp++;
            n--;
            if (n * m == 0) break;

            for (int p = 0; p < n; p++)//从上自下
                arr[i=i+1][j] = temp++;
            m--;
            if (n * m == 0) break;

            for (int p = 0; p < m; p++)//从右自左
                arr[i][j=j-1] = temp++;
            n--;
            if (n * m == 0) break;

            for (int p = 0; p < n; p++)//从下自上
                arr[i=i-1][j] = temp++;
            m--;
     }

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【洛谷】P5731