Generate Div Tags

• Time : O(n!)
• Space : O(n!)

#include <vector>
using namespace std;

const string OPEN = "<div>";
const string CLOSE = "</div>";

void helper(vector<string>& res, int o, int c, int now, string& tmp) {
	if(o + c == 0) {
		string s;
		for(auto& ch : tmp) {
			if(ch == '0') s += OPEN;
			else s += CLOSE;
		}
		res.push_back(s);
		return;
	}
	if(o) {
		tmp.push_back('0');
		helper(res, o - 1, c, now + 1, tmp);
		tmp.pop_back();
	}
	if(c and now) {
		tmp.push_back('1');
		helper(res, o, c - 1, now - 1, tmp);
		tmp.pop_back();
	}
}

vector<string> generateDivTags(int n) {
  vector<string> res;
	string tmp;
	helper(res, n, n, 0, tmp);
  return res;
}