diff --git a/gamedata.cpp b/gamedata.cpp
index 951b49e..e7699ca 100644
--- a/gamedata.cpp
+++ b/gamedata.cpp
@@ -1,5 +1,10 @@
 #include "gamedata.h"
 #include "mathutils.h"
+#include "debug.h"
+#include <list>
+#include <algorithm>
+
+using std::list;
 
 int GameData::PLAYER1_COLOUR = 0x4a483f;
 int GameData::PLAYER2_COLOUR = 0x090c7a;
@@ -58,6 +63,10 @@ bool GameData::add_vertex(int x, int y, int r, int colour)
 	    (player == PLAYER2 && !player2_played))
 	{
 	    Graph::add_vertex(x, y, r, colour, 10);
+#ifdef DEBUG
+	fprintf(stderr, "debug: GameData::add_vertex(): strength=%d\n",
+		calculate_strength(*(vertices.rbegin())));
+#endif
 	    if (player == PLAYER1) player1_played = true;
 	    if (player == PLAYER2) player2_played = true;
 	    toggle_turn();
@@ -68,9 +77,69 @@ bool GameData::add_vertex(int x, int y, int r, int colour)
 
     if (Graph::add_vertex(x, y, r, colour, 10, current))
     {
+#ifdef DEBUG
+	fprintf(stderr, "debug: GameData::add_vertex(): strength=%d\n",
+		calculate_strength(*(vertices.rbegin())));
+#endif
+
 	clear_current_vertex();
 	toggle_turn();
 	return true;
     }
     return false;
 }
+
+
+// Oh the recursive recursion!
+unsigned int GameData::calculate_strength(Vertex* node, unsigned int depth, list<Vertex*>* visited)
+{
+    if (visited == NULL) visited = new list<Vertex*>;
+    visited->push_back(node);
+
+    list<Vertex*> all_nodes = get_colour(node->colour);
+
+    // Special case - a one-node tree just returns its own score!
+    if (all_nodes.size() == 1) return node->score;
+
+
+    // Find which vertices we need to visit from here
+    list<Edge> es = get_vertex_edges(node);
+    list<Vertex*> to_visit;
+
+    for (list<Edge>::iterator cursor = es.begin(); cursor != es.end();
+	 cursor++)
+    {
+	Edge e = *cursor;
+	// if this is true, we haven't visited the vertex on the other end of
+	// this edge yet
+	if (e.a == node &&
+	    find(visited->begin(), visited->end(), e.b) == visited->end())
+	{
+	    to_visit.push_back(e.b);
+	}
+	else if (e.a == node &&
+		 find(visited->begin(), visited->end(), e.b) == visited->end())
+	{
+	    to_visit.push_back(e.a);
+	}
+    }
+
+    // This is the base case - this node has no unvisited neighbors
+    if (to_visit.empty()) return node->score / depth;
+
+    // Else, iterate through to_visit and visit them all, summing their
+    // effective strengths adjusted for depth.
+    // Since our trees are acyclic, this can't loop.
+    int modscore = node->score;
+    if (depth > 0) modscore /= depth;
+
+    for (list<Vertex*>::iterator cursor = to_visit.begin();
+	 cursor != to_visit.end(); cursor++)
+    {
+	Vertex* v = *cursor;
+	modscore += calculate_strength(v, depth+1, visited);
+    }
+
+    if (depth == 0) delete visited;
+    return modscore;
+}
diff --git a/gamedata.h b/gamedata.h
index 979b007..7f6c8bf 100644
--- a/gamedata.h
+++ b/gamedata.h
@@ -29,6 +29,8 @@ class GameData : public Graph
     bool add_vertex(int x, int y, int r, int colour);
 
  private:
+    unsigned int calculate_strength(Vertex* node, unsigned int depth = 0, list<Vertex*>* visited = NULL);
+
     Vertex* current;
     Turn player;
     bool player1_played;
diff --git a/graph.cpp b/graph.cpp
index 9608c0c..1823eca 100644
--- a/graph.cpp
+++ b/graph.cpp
@@ -106,7 +106,7 @@ bool Graph::add_vertex(int x, int y, int r, int colour, int score, Vertex* src)
     vertices.push_back(v);
 
 #ifdef DEBUG
-    fprintf(stderr, "debug: Graph::add_vertex(): added: x=%d, y=%d, r=%d\n", v->x, v->y, v->r);
+    fprintf(stderr, "debug: Graph::add_vertex(): added: x=%d, y=%d, r=%d, score=%d\n", v->x, v->y, v->r, v->score);
 #endif
 
     return true;
@@ -121,3 +121,33 @@ Vertex::Vertex(int x, int y, int r, int colour, int score)
     this->colour = colour;
     this->score = score;
 }
+
+
+list<Vertex*> Graph::get_colour(int colour)
+{
+    list<Vertex*> answer;
+
+    for (list<Vertex*>::iterator cursor = vertices.begin();
+	 cursor != vertices.end(); cursor++)
+    {
+	Vertex* v = *cursor;
+	if (v->colour == colour) answer.push_back(v);
+    }
+
+    return answer;
+}
+
+
+list<Edge> Graph::get_vertex_edges(Vertex* v)
+{
+    list<Edge> answer;
+
+    for (list<Edge>::iterator cursor = edges.begin();
+	 cursor != edges.end(); cursor++)
+    {
+	Edge e = *cursor;
+	if (e.a == v || e.b == v) answer.push_back(e);
+    }
+
+    return answer;
+}
diff --git a/graph.h b/graph.h
index 04b3151..e94c379 100644
--- a/graph.h
+++ b/graph.h
@@ -48,6 +48,8 @@ class Graph
 
     list<Vertex*> get_vertices() const { return vertices; }
     list<Edge> get_edges() const { return edges; }
+    list<Vertex*> get_colour(int colour);
+    list<Edge> get_vertex_edges(Vertex* v);
 
     bool point_in_vertex(int x, int y, int size);
     Vertex * vertex_at(int x, int y);