Leetcode 54：螺旋矩阵I

整体思路是按题目要求模拟，顺时针转，先从左到右，再从上到下
最后从右到左，从下到上，注意点在于边界值控制

Code

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
       if(matrix.empty() || matrix[0].empty())
       {
           return {};
       }
       int m = matrix.size();
       int n = matrix[0].size();

       int up = 0,left = 0;
       int down = m-1,right = n-1;

       ventor<int> res;

       while(up<=down && left<=right)
       {
           for(int i = left;i <= right;i++)    // 注意<= [left,right]
           {
               res.push_back(matrix[up][i]);
           }
           for(int i = up + 1;i <= down;i++)   //注意+1 <= (up,down]
           {
               res.push_back(matrix[i][right]);
           }
           if(up<down && left<right)
           //当up==down的时候我们实际上只有一行要输出，上面已经输出了
           {
               for(int i = right - 1;i > left;i--)  //[right,left)
               {
                    res.push_back(matrix[down][i]);
               }
               for(int i = down;i > up;i--)        //(down,up)
               {
                    res.push_back(matrix[i][left]);
               }
           }
       }
        return res;
    }

};