grapht: add get_reachable function

This simply performs a depth-first search of the graph starting from
a nominated node and returns a vector of reachable indices.

Author: smowton

src/util/graph.h

@@ -246,6 +246,8 @@ class grapht
 
   void visit_reachable(node_indext src);
 
+  std::vector<node_indext> get_reachable(node_indext src, bool forwards) const;
+
   void make_chordal();
 
   // return value: number of connected subgraphs
@@ -447,26 +449,40 @@ void grapht<N>::shortest_path(
 template<class N>
 void grapht<N>::visit_reachable(node_indext src)
 {
-  // DFS
+  std::vector<node_indext> reachable = get_reachable(src, true);
+  for(const auto index : reachable)
+    nodes[index].visited = true;
+}
+
+template<class N>
+std::vector<typename N::node_indext>
+grapht<N>::get_reachable(node_indext src, bool forwards) const
+{
+  std::vector<node_indext> result;
+  std::vector<bool> visited(size(), false);
 
-  std::stack<node_indext> s;
+  std::stack<node_indext, std::vector<node_indext>> s;
   s.push(src);
 
   while(!s.empty())
   {
-    node_indext n=s.top();
+    node_indext n = s.top();
     s.pop();
 
-    nodet &node=nodes[n];
-    node.visited=true;
+    if(visited[n])
+      continue;
 
-    for(typename edgest::const_iterator
-        it=node.out.begin();
-        it!=node.out.end();
-        it++)
-      if(!nodes[it->first].visited)
-        s.push(it->first);
+    result.push_back(n);
+    visited[n] = true;
+
+    const auto &node = nodes[n];
+    const auto &succs = forwards ? node.out : node.in;
+    for(const auto succ : succs)
+      if(!visited[succ.first])
+        s.push(succ.first);
   }
+
+  return result;
 }
 
 template<class N>