Added random selection policy

source/MoleculeAutoCorrect.hpp

@@ -618,17 +618,18 @@ struct Constant {
 }; // ! MoleculeAutoCorrect::Policy::Objective namespace
 
 
-// Virtually all policies can be expressed as a GreedyPolicy, provided that we
-// adjust the objective on which the GreedyPolicy selects and tries to maximize.
 enum class Type {
   BFS,
   Familiarity,
   DistanceNormalizedFamiliarity,
   Astar,
   UCT,
-  MLR
+  MLR,
+  Random
 };
 
+// Virtually all policies can be expressed as a GreedyPolicy, provided that we
+// adjust the objective on which the GreedyPolicy selects and tries to maximize.
 struct BFS : GreedyPolicy<Vertex> {
   BFS(const RDKit::ROMol& root_molecule) : 
     GreedyPolicy<Vertex>(Objective::TopologicalSimilarity(root_molecule)) {};
@@ -675,6 +676,8 @@ struct ObjectivePreservation : GreedyPolicy<Vertex> {
       Objective::Wrapper(Objective::MoleculeObjective(objective))) {};
 };
 
+typedef RandomPolicy<Vertex> Random;
+
 struct Dummy : GreedyPolicy<Vertex> {
   Dummy(double x) : GreedyPolicy<Vertex>(Objective::Constant(x)) {};
 };

source/TreeSearch.hpp

@@ -4,6 +4,7 @@
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/dynamic_bitset.hpp>
 #include <concepts>
+#include <random>
 #include <queue>
 #include <cmath>
 
@@ -377,5 +378,41 @@ class UpperConfidenceTree {
   };
 };
 
+template <class Vertex>
+class RandomPolicy {
+  typedef TreeSearch<Vertex>::Tree Tree;
+  std::mt19937 prng;
+
+public:
+  RandomPolicy() {
+    std::random_device rd;
+    prng.seed(rd());
+  };
+
+  RandomPolicy(std::mt19937::result_type seed) {
+    prng.seed(seed);
+  };
+
+  std::pair<typename Tree::vertex_descriptor, bool> operator()(
+    const TreeSearch<Vertex>& tree_search) {
+    const Tree& tree = tree_search.GetTree();
+    const auto& vertex_expandable = tree_search.GetExpandableVerticesMask();
+    std::size_t n_vertices = boost::num_vertices(tree);
+    if (n_vertices < 2) {
+      return {0, n_vertices ? vertex_expandable[0] : false};
+    };
+    std::uniform_int_distribution<std::size_t> distribution (0, n_vertices - 1);
+    std::size_t vertex_idx = distribution(prng);
+    for (std::size_t i = 0; i < n_vertices; ++i) {
+      if (vertex_expandable[vertex_idx]) {
+        return {vertex_idx, true};
+      };
+      if (++vertex_idx >= n_vertices) {
+        vertex_idx = 0;
+      };
+    };
+    return {0, false};
+  };
+};
 
 #endif // !_TREE_SEARCH_HPP_