数字字符串转化成IP地址_牛客题霸_牛客网现在有一个只包含数字的字符串，将该字符串转化成IP地址的形式，返回所有可能的情况。。题目来自【牛客题霸】https://www.nowcoder.com/practice/ce73540d47374dbe85b3125f57727e1e?tpId=295&tags=&title=&difficulty=0&judgeStatus=0&rp=0&sourceUrl=%2Fexam%2Foj%3Fpage%3D1%26tab%3D%25E7%25AE%2597%25E6%25B3%2595%25E7%25AF%2587%26topicId%3D295

vector<string> restoreIpAddresses(string s) {
	// write code here
	int n = s.size();

	vector<string> res;

	for (int i = 1; i < 4 && i < n - 2; ++i)
	{
		for (int j = i + 1; j < i + 4 && j < n - 1; ++j)
		{
			for (int k = j + 1; k < j + 4 && k < n; ++k)
			{
				if (k < n - 3)
				{
					continue;
				}
				
				string a = s.substr(0, i);
				string b = s.substr(i, j - i);
				string c = s.substr(j, k - j);
				string d = s.substr(k);

				if (stoi(a) > 255 || stoi(b) > 255 || stoi(c) > 255 || stoi(d) > 255)
				{
					continue;
				}
				if ((a.size() > 1 && a.front() == '0') || (b.size() > 1 && b.front() == '0')
					|| (c.size() > 1 && c.front() == '0') || (d.size() > 1 && d.front() == '0'))
				{
					continue;
				}

				res.push_back(a + '.' + b + '.' + c + '.' + d);
			}
		}
	}
	
	return res;
}