LeetCode Spiral Matrix II

怎么做了好几个题都没什么含金量呢，刷的感觉

vector<vector<int> > generateMatrix(int n) {
	vector<vector<int> > ret;
	if (n==0)
	{
		return ret;
	}
	vector<int> temp;
	for (int i=0;i<n;i++)
	{
		temp.clear();
		for (int j=0;j<n;j++)
		{
			temp.push_back(0);
		}
		ret.push_back(temp);
	}
	
	int left=0,up = 0,down = n-1 , right= n-1;
	int i,j;
	int num = 0;
	while(left<=right&&up<=down)
	{
		i = up;
		j = left;
		while(i>=up&&i<=down&&j>=left&&j<=right)
		{
			ret[i][j] = ++num;
			j++;
		}
		up++;
		i = up;
		j = right;
		while(i>=up&&i<=down&&j>=left&&j<=right)
		{
			ret[i][j] = ++num;
			i++;
		}
		right--;
		i = down;
		j =right;
		while(i>=up&&i<=down&&j>=left&&j<=right)
		{
			ret[i][j] = ++num;
			j--;
		}
		down--;
		i = down;
		j = left;
		while(i>=up&&i<=down&&j>=left&&j<=right)
		{
			ret[i][j] = ++num;
			i--;
		}
		left++;
	}
	return ret;
}