顺时针打印矩阵

vector<int> printMatrix(vector<vector<int> > matrix) {
	int rows = matrix.size();
    int cols = matrix[0].size();
    vector<int> res;
    if(rows == 0 || cols == 0)
        return res;
    
    int left = 0,right = cols - 1,top = 0,bottom = rows - 1;
    while(left <= right && top <= bottom){
        for(int i = left; i <= right; ++i)
            res.push_back(matrix[top][i]);
        for(int i = top + 1; i <= bottom; ++i)
            res.push_back(matrix[i][right]);
        if(top != bottom){
        	for(int i = right - 1; i >= left; --i)
           		res.push_back(matrix[bottom][i]);
        }
        if(left != right){
        	for(int i = bottom - 1; i > top; --i)
            	res.push_back(matrix[i][left]);
        }
        ++left,--right,++top,--bottom;
    }
    return res;
}