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模拟题
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螺旋矩阵
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给定一个m x n大小的矩阵（m行，n列），按螺旋的顺序返回矩阵中的所有元素。 [#matrix]_

.. code-block:: cpp

   class Solution {
   public:
      vector<int> spiralOrder(vector<vector<int> > &matrix) {
         if(matrix.size() == 0) return {};
         vector<int> result;
         int         top = 0, bottom = matrix.size() - 1;
         int         left = 0, right = matrix[0].size() - 1;
         while(top <= matrix.size() / 2 && left <= matrix[0].size() / 2) {
               // top l -> r
               for(int i = left; i <= right; ++i) result.push_back(matrix[top][i]);
               // left top -> bottom
               for(int i = top + 1; i <= bottom; ++i) result.push_back(matrix[i][right]);
               // bottom r -> l
               for(int i = right - 1; top != bottom && i >= left; --i) result.push_back(matrix[bottom][i]);
               // l bottom -> top
               for(int i = bottom - 1; left != right && i >= top + 1; --i) result.push_back(matrix[i][left]);
               ++top;
               --bottom;
               ++left;
               --right;
         }
         return {result.begin(), result.begin() + matrix.size()*matrix[0].size()};
      }
   };

.. [#matrix] `螺旋矩阵 <https://blog.nowcoder.net/n/1e3dba4db16b4243bf858cf3fc515b6e>`_