algo: simplify regular equations solver

alib2algo/src/equations/RegularEquationSolver.h

@@ -189,14 +189,10 @@ void RegularEquationSolver < TerminalSymbolType, VariableSymbolType >::addEquati
 template < class TerminalSymbolType, class VariableSymbolType >
 void RegularEquationSolver < TerminalSymbolType, VariableSymbolType >::sortSymbolsByDepth ( const VariableSymbolType & solveFor ) {
-	ext::map < VariableSymbolType, bool > visited;
+	ext::set < VariableSymbolType > visited;
 	std::queue < VariableSymbolType > queue;
-	for(const VariableSymbolType & symbol : nonterminalSymbols ) {
-		visited [ symbol ] = false;
-	}
-
-	visited [ solveFor ] = true;
+	visited.insert ( solveFor );
 	queue.push ( solveFor );
 	while ( ! queue.empty ( ) ) {
@@ -205,13 +201,10 @@ void RegularEquationSolver < TerminalSymbolType, VariableSymbolType >::sortSymbo
 		nonterminalSymbolsByDepth.push_back ( variable );
-		for ( const auto & kv : equationTransition ) {
+		for ( const auto & kv : equationTransition )
 			// find all transitions from current symbol that are non-empty, enqueue transition'variable target symbol
-			if ( kv.first.first == variable && ! visited [ kv.first.second ] && !kv.second.getElements ( ).empty ( ) ) {
-				visited [ kv.first.second ] = true;
+			if ( kv.first.first == variable && !kv.second.getElements ( ).empty ( ) && visited.insert ( kv.first.second ).second )
 				queue.push ( kv.first.second );
-			}
-		}
 	}
 }