[LeetCode] Remove All Adjacent Duplicates in String II

string removeDuplicates(string str, int k) 
{
	stack<pair<char, int>> s;
	auto begin = str.begin(), end = str.end();

	while (begin != end)
	{
		auto ch = *begin;

		if (!s.empty())
		{
			auto& top = s.top();

			if (top.first != ch)
				s.push({ ch, 1 });

			else
				top.second++;

			if (top.second == k)
				s.pop();
		}
		else
			s.push({ ch, 1 });

		begin++;
	}
	str.clear();

	while (!s.empty())
	{
		auto top = s.top();

		for (int i = 0; i < top.second; i++)
			str.push_back(top.first);

		s.pop();
	}
	reverse(str.begin(), str.end());
	return str;
}