ADDED   lib/graph/dfa_hopcroft.cpp
Index: lib/graph/dfa_hopcroft.cpp
==================================================================
--- lib/graph/dfa_hopcroft.cpp
+++ lib/graph/dfa_hopcroft.cpp
@@ -0,0 +1,111 @@
+// TODO : optimize to O(n log n)
+//  current version looks to be running in O(n^2) ... orz
+//
+// TODO : clean up as a library
+//
+// Copy&Paste from SRM562 Div1 Hard
+
+	// Input is given as:
+	//    v----c---->G[v][c]
+	// Must be a complete automaton.
+	// !!! The following code is assuming |c|==4 !!!
+	//
+	// !!! The following code is assuming the final state is {0}.
+	//
+	mint solve(vector< vector<int> >& G)
+	{
+		vector< vector<int> > set_buffer;
+		set<int> active_sets;
+		set<int> active_splitters;
+
+		{
+			set_buffer.push_back( vector<int>(1,0) );
+			vector<int> all;
+			for(int v=1; v<G.size(); ++v)
+				all.push_back(v);
+			set_buffer.push_back(all);
+
+			active_sets.insert(0);
+			active_sets.insert(1);
+			active_splitters.insert(0);
+		}
+
+		while(!active_splitters.empty())
+		{
+			const vector<int>& splv = set_buffer[*active_splitters.begin()];
+			set<int> spl(splv.begin(), splv.end());
+			active_splitters.erase(active_splitters.begin());
+
+			for(int d=0; d<4; ++d)
+			for(set<int>::iterator it=active_sets.begin(); it!=active_sets.end(); )
+			{
+				int ii = *it++;
+				const vector<int>& cur = set_buffer[ii];
+				vector<int> t, f;
+				for(int k=0; k<cur.size(); ++k)
+					(spl.count(G[cur[k]][d]) ? t : f).push_back(cur[k]);
+				if(!t.empty() && !f.empty())
+				{
+					set_buffer.push_back(t);
+					set_buffer.push_back(f);
+					active_sets.insert(set_buffer.size()-2);
+					active_sets.insert(set_buffer.size()-1);
+					if(active_splitters.count(ii)) {
+						active_splitters.insert(set_buffer.size()-2);
+						active_splitters.insert(set_buffer.size()-1);
+					} else {
+						active_splitters.insert(t.size()<f.size() ? set_buffer.size()-2 : set_buffer.size()-1);
+					}
+					active_splitters.erase(ii);
+					active_sets.erase(ii);
+				}
+			}
+		}
+
+		vector<int> es;
+		for(set<int>::iterator it=active_sets.begin(); it!=active_sets.end(); ++it)
+			if(*it)
+				es.push_back(set_buffer[*it].size());
+/*
+		for(bool changed=true; changed;) 
+		{
+			changed=false;
+			for(int i=0; i<eqs.size(); ++i) if(!eqs[i].second && !dead[i]){
+				set<int> spl(eqs[i].first.begin(), eqs[i].first.end());
+				eqs[i].second = true;
+				for(int k=0; k<eqs.size(); ++k)
+				for(int d=0; d<4; ++d) if(!dead[k]) {
+					vector<int> t, f;
+					for(vector<int>::iterator it=eqs[k].first.begin(); it!=eqs[k].first.end(); ++it)
+						(spl.count(G[*it][d]) ? t : f).push_back(*it);
+					if(!t.empty() && !f.empty()) {
+						if(eqs[k].second) {
+							eqs.push_back(make_pair(t,t.size()>f.size()));
+							eqs.push_back(make_pair(f,t.size()<=f.size()));
+							dead.push_back(false);
+							dead.push_back(false);
+							changed = true;
+						} else {
+							eqs.push_back(make_pair(t,false));
+							eqs.push_back(make_pair(f,false));
+							dead.push_back(false);
+							dead.push_back(false);
+							changed = true;
+						}
+						dead[k] = true;
+					}
+				}
+			}
+		}
+
+		vector<int> es;
+		for(int i=1; i<eqs.size(); ++i) if(!dead[i]) 
+			es.push_back(eqs[i].first.size());
+*/
+		int sum = accumulate(es.begin(), es.end(), 0);
+		mint x = POW(2, sum);
+		for(int i=0; i<es.size(); ++i)
+			x -= POW(2, es[i])-1;
+		return x-1;
+	}
+