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 {
public:
    vector<int> printMatrix(vector<vector<int> > matrix) {
        vector<int> res;
        int row=matrix.size();
        if(row==0) return  res;
        int col=matrix[0].size();
        int i,j,left=0,right=col-1,up=0,down=row-1;
        while(left<=right&&up<=down)
        {
            //上行
            for(j=left;j<=right;j++)
                res.push_back(matrix[up][j]);
            //右列
            for(i=up+1;i<=down;i++)
                res.push_back(matrix[i][right]);
            //下行
            if(down>up)
                for(j=right-1;j>=left;j--)
                    res.push_back(matrix[down][j]);
            //左列
            if(left<right)
                for(i=down-1;i>up;i--)
                    res.push_back(matrix[i][left]);
            up++;
            down--;
            left++;
            right--;
        }
        return res;
    }
};