leetcode - Missing Ranges

称号：

Missing Ranges

Given a sorted integer array where the range of elements are [0, 99]inclusive, return its missing ranges.
For example, given [0, 1, 3, 50, 75], return[“2”, “4->49”, “51->74”, “76->99”]

void generate_string(int l, int r, vector<string> &res)
{
	if (l>r || l < 0 || r>99)
		return;
	if (l == r)
		res.push_back(to_string(l));
	else
	{
		string s1 = to_string(l),s2="->",s3=to_string(r);
		res.push_back(s1+s2+s3);
	}
}

vector<string> MissingRanges(const vector<int> &nums)
{
	vector<string> res;

	if (nums.empty())
	{
		generate_string(0, 99, res);
		return res;
	}

	if (nums.size() == 1)
	{
		generate_string(0, nums[0]-1, res);
		generate_string(nums[0]+1, 99, res);
		return res;					
	}

	generate_string(0, nums[0] - 1, res);
	for (int i = 1; i < nums.size(); ++i)
	{
		generate_string(nums[i-1]+1, nums[i] - 1, res);
	}
	generate_string(nums.back()+1, 99, res);

	return res;

}