leetcode 97. Interleaving String

Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.

For example,
Given:
s1 = "aabcc",
s2 = "dbbca",

When s3 = "aadbbcbcac", return true.
When s3 = "aadbbbaccc", return false.

class Solution {
	bool do_once(vector<pair<pair<string, string>, string>>&candi, set<pair<pair<string, string>, string>>&history)
	{
		vector<pair<pair<string, string>, string>>newcandi;
		for (int i = 0; i < candi.size(); i++)
		{
			string s1 = candi[i].first.first;
			string s2 = candi[i].first.second;
			string s3 = candi[i].second;
			for (int j = s1.length()-1; j >=0; j--)
			{
				if (string(s1.begin(), s1.begin() + j + 1) != string(s3.begin(), s3.begin() + j + 1))
					continue;
				if (j == s1.length() - 1)
				{
					if (s3 == s1 + s2)
						return true;
					continue;
				}
				string ss1 = string(s1.begin() + j + 1, s1.end());
				string ss2 = s2;
				string ss3 = string(s3.begin() + j + 1, s3.end());
				if (history.find(pair<pair<string, string>, string>(pair<string, string>(ss1, ss2), ss3)) == history.end())
				{
					newcandi.push_back(pair<pair<string, string>, string>(pair<string, string>(ss1, ss2), ss3));
					history.insert(pair<pair<string, string>, string>(pair<string, string>(ss1, ss2), ss3));
				}
			}
			for (int j = s2.length()-1; j >=0; j--)
			{
				if (string(s2.begin(), s2.begin() + j + 1) != string(s3.begin(), s3.begin() + j + 1))
					continue;
				if (j == s2.length() - 1)
				{
					if (s3 == s2 + s1)
						return true;
					continue;
				}
				string ss2 = string(s2.begin() + j + 1, s2.end());
				string ss1 = s1;
				string ss3 = string(s3.begin() + j + 1, s3.end());
				if (history.find(pair<pair<string, string>, string>(pair<string, string>(ss1, ss2), ss3)) == history.end())
				{
					newcandi.push_back(pair<pair<string, string>, string>(pair<string, string>(ss1, ss2), ss3));
					history.insert(pair<pair<string, string>, string>(pair<string, string>(ss1, ss2), ss3));
				}
			}
		}
		candi = newcandi;
		return false;
	}
public:
	bool isInterleave(string s1, string s2, string s3) {
		if (s3.length() != s1.length() + s2.length())
			return false;
		map<char, int>m1, m2;
		for (int i = 0; i < s1.length(); i++)
			m1[s1[i]]++;
		for (int i = 0; i < s2.length(); i++)
			m1[s2[i]]++;
		for (int i = 0; i < s3.length(); i++)
			m2[s3[i]]++;
		if (m1 != m2)
			return false;
		if (s1.empty() && s2.empty() && s3.empty())
			return true;
		vector<pair<pair<string, string>, string>>candi;
		set<pair<pair<string, string>, string>>history;
		candi.push_back(pair<pair<string, string>, string>(pair<string, string>(s1, s2), s3));
		bool f = false;
		while (!f&&!candi.empty())
		{
			f = do_once(candi,history);
		}
		return f;
	}
};

accepted