Split Text Message.cpp

class Solution
{
public:
	vector<string> split(const string& message, int limit)
	{
		int len = message.size(), k = len % limit ? len / limit + 1 : len / limit, digitsOfN = to_string(k).size();
		vector<string> res;
		while (!canSplit(message, limit, digitsOfN, res))++digitsOfN;
		return res;
	}

private:
	bool canSplit(const string& message, int limit, int digitsOfN, vector<string>& res)
	{
		//calculate length of (?/n)
		int helper = digitsOfN + 3, i = 0;
		//try to split with current digitsOfN
		while (i < message.size())
		{
			int cnt = res.size() + 1, padding = to_string(cnt).size() + helper, step = limit - padding;
			string str;
			if (i + step >= message.size())
			{
				str = message.substr(i);
				i += step;
			}
			else
			{
				int j = i + step;
				while (message[j] != ' ')--j;
				str = message.substr(i, j - i);
				i = j + 1;
			}
			res.push_back(str);
			++cnt;
		}
		int n = res.size();
		if (to_string(n).size() == digitsOfN)
		{
			for (int i = 1; i <= n; ++i)
			{
				string info = "(" + to_string(i) + "/" + to_string(n) + ")";
				res[i - 1] += info;
			}
			return true;
		}
		res.clear();
		return false;
	}
};