顺时针打印矩阵

 输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字，例如，如果输入如下矩阵： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.
 1 class Solution {
 2 public:
 3     vector<int> printMatrix(vector<vector<int> > matrix) {
 4         vector<int> res;
 5         int row=matrix.size();
 6         if(row==0) return  res;
 7         int col=matrix[0].size();
 8         int i,j,left=0,right=col-1,up=0,down=row-1;
 9         while(left<=right&&up<=down)
10         {
11             //上行
12             for(j=left;j<=right;j++)
13                 res.push_back(matrix[up][j]);
14             //右列
15             for(i=up+1;i<=down;i++)
16                 res.push_back(matrix[i][right]);
17             //下行
18             if(down>up)
19                 for(j=right-1;j>=left;j--)
20                     res.push_back(matrix[down][j]);
21             //左列
22             if(left<right)
23                 for(i=down-1;i>up;i--)
24                     res.push_back(matrix[i][left]);
25             up++;
26             down--;
27             left++;
28             right--;
29         }
30         return res;
31     }
32 };