From 31f88a55796cfb7c49acc105b2a3b6c57e0a60ed Mon Sep 17 00:00:00 2001
From: Theodore Turocy <ted.turocy@gmail.com>
Date: Tue, 16 Dec 2025 16:03:58 +0000
Subject: [PATCH 1/2] Implement collection of players including chance.

This adds a convenience collection `GetPlayersWithChance`, which allows for
iteration over all players, with the object representing
the chance player first in the iteration.
---
 src/core/util.h       | 54 +++++++++++++++++++++++++++++++++++++++++++
 src/games/behavspt.cc |  3 +--
 src/games/game.h      |  1 +
 3 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/src/core/util.h b/src/core/util.h
index f5678c706..fa33f5384 100644
--- a/src/core/util.h
+++ b/src/core/util.h
@@ -135,6 +135,60 @@ template <typename Container, typename T> class exclude_value {
   iterator m_begin, m_end;
 };
 
+template <typename Value, typename Range> class prepend_value {
+public:
+  using Iter = decltype(std::begin(std::declval<Range &>()));
+
+  class iterator {
+  public:
+    using iterator_category = std::forward_iterator_tag;
+    ;
+    using value_type = Value;
+    using difference_type = std::ptrdiff_t;
+    using reference = Value;
+    using pointer = Value;
+
+    iterator(std::optional<Value> first, Iter current, Iter end)
+      : m_first(std::move(first)), m_current(current), m_end(end)
+    {
+    }
+
+    reference operator*() const { return m_first ? *m_first : *m_current; }
+
+    iterator &operator++()
+    {
+      if (m_first) {
+        m_first.reset();
+      }
+      else {
+        ++m_current;
+      }
+      return *this;
+    }
+
+    bool operator==(const iterator &other) const
+    {
+      return m_first == other.m_first && m_current == other.m_current;
+    }
+
+    bool operator!=(const iterator &other) const { return !(*this == other); }
+
+  private:
+    std::optional<Value> m_first;
+    Iter m_current, m_end;
+  };
+
+  prepend_value(Value first, Range range) : m_first(first), m_range(std::move(range)) {}
+
+  iterator begin() const { return {m_first, std::begin(m_range), std::end(m_range)}; }
+
+  iterator end() const { return {std::nullopt, std::end(m_range), std::end(m_range)}; }
+
+private:
+  Value m_first;
+  Range m_range;
+};
+
 /// @brief Returns the maximum value of the function over the *non-empty* container
 template <class Container, class Func>
 auto maximize_function(const Container &p_container, const Func &p_function)
diff --git a/src/games/behavspt.cc b/src/games/behavspt.cc
index 81cd29c9f..95f055b97 100644
--- a/src/games/behavspt.cc
+++ b/src/games/behavspt.cc
@@ -40,8 +40,7 @@ BehaviorSupportProfile::BehaviorSupportProfile(const Game &p_efg) : m_efg(p_efg)
   }
 
   // Initialize the list of reachable information sets and nodes
-  for (size_t pl = 0; pl <= GetGame()->NumPlayers(); pl++) {
-    const GamePlayer player = (pl == 0) ? GetGame()->GetChance() : GetGame()->GetPlayer(pl);
+  for (const auto &player : p_efg->GetPlayersWithChance()) {
     for (const auto &infoset : player->GetInfosets()) {
       m_infosetReachable[infoset] = true;
       for (const auto &member : infoset->GetMembers()) {
diff --git a/src/games/game.h b/src/games/game.h
index 4ff655df8..e060fb061 100644
--- a/src/games/game.h
+++ b/src/games/game.h
@@ -936,6 +936,7 @@ class GameRep : public std::enable_shared_from_this<GameRep> {
   }
   /// Returns the chance (nature) player
   virtual GamePlayer GetChance() const = 0;
+  auto GetPlayersWithChance() const { return prepend_value(GetChance(), GetPlayers()); }
   /// Creates a new player in the game, with no moves
   virtual GamePlayer NewPlayer() = 0;
   //@}

From 89373d7310386cab7dcbf797b5cd5395871a2ddd Mon Sep 17 00:00:00 2001
From: Theodore Turocy <ted.turocy@gmail.com>
Date: Tue, 16 Dec 2025 16:19:01 +0000
Subject: [PATCH 2/2] Include header <optional>

---
 src/core/util.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/core/util.h b/src/core/util.h
index fa33f5384..1607f1fa1 100644
--- a/src/core/util.h
+++ b/src/core/util.h
@@ -30,6 +30,7 @@
 #include <algorithm>
 #include <numeric>
 #include <map>
+#include <optional>
 
 namespace Gambit {