DFS: Change second variant to also offer canceling of traversal

alib2algo/src/graph/traverse/Dfs.cpp

@@ -42,18 +42,20 @@ static void dfs_impl(const T &graph, const Node &start, Dfs::Function func)
 }
 template <typename T>
-static void dfs2_impl(const T &graph, const Node &n, const Node &p, std::unordered_map<Node, bool> &visited, int &time, Dfs::FunctionExt func)
+static bool dfs2_impl(const T &graph, const Node &n, const Node &p, std::unordered_map<Node, bool> &visited, int &time, Dfs::FunctionExt func)
 {
 	int opened = ++time;
 	visited[n] = true;
 	for (const Node &e : graph.neighbors(n)) {
 		if (visited.find(e) == visited.end()) {
-			dfs2_impl(graph, e, n, visited, time, func);
+			if (!dfs2_impl(graph, e, n, visited, time, func)) {
+				return false;
+			}
 		}
 	}
-	func(n, p, opened, ++time);
+	return func(n, p, opened, ++time);
 }
 void Dfs::dfs(const Graph &graph, const Node &start, Dfs::Function func)

alib2algo/src/graph/traverse/Dfs.h

@@ -14,13 +14,13 @@ namespace traverse
 // func is called for each visited node, traversal stops when returning false
 //
 // bool Function(const Node &node);
-// void FunctionExt(const Node &node, const Node &predecessor, int openTime, int closeTime);
+// bool FunctionExt(const Node &node, const Node &predecessor, int openTime, int closeTime);
 class Dfs : public graph::VisitableGraphBase::const_visitor_type
 {
 public:
 	typedef std::function<bool(const Node&)> Function;
-	typedef std::function<void(const Node&, const Node&, int, int)> FunctionExt;
+	typedef std::function<bool(const Node&, const Node&, int, int)> FunctionExt;
 	static void dfs(const Graph &graph, const Node &start, Function func);
 	static void dfs(const Graph &graph, const Node &start, FunctionExt func);

alib2algo/test-src/graph/traverse/DfsTest.cpp

@@ -188,6 +188,7 @@ void GraphDfsTest::testDfs2()
 		opened[n] = o;
 		closed[n] = c;
 		predecessors[n] = p;
+		return true;
 	});
 	CPPUNIT_ASSERT_EQUAL(5, counter);
@@ -216,6 +217,7 @@ void GraphDfsTest::testDfs2()
 		opened[n] = o;
 		closed[n] = c;
 		predecessors[n] = p;
+		return true;
 	});
 	CPPUNIT_ASSERT_EQUAL(5, counter);