From aa32d81f8da39e4456a91c244c8a8c2fad1e05fc Mon Sep 17 00:00:00 2001
From: Mark Bluemer <bluemer.mark@gmail.com>
Date: Wed, 19 Apr 2017 20:31:20 -0400
Subject: [PATCH] Added alpha-beta... still getting seg faults

---
 include/MinimaxSearch.h |  3 ++-
 src/MinimaxSearch.cpp   | 31 +++++++++++++++++++++++++++++--
 src/main.cpp            |  2 +-
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/include/MinimaxSearch.h b/include/MinimaxSearch.h
index 53413df..9665a54 100644
--- a/include/MinimaxSearch.h
+++ b/include/MinimaxSearch.h
@@ -10,10 +10,11 @@
 class MinimaxSearch
 {
 private:
-  static const int maxDepth = 7;
+  static const int maxDepth = 6;
 
   double minValue(std::unique_ptr<BitBoard> &board, int currentDepth) const;
   double maxValue(std::unique_ptr<BitBoard> &board, int currentDepth) const;
+  double alphaBeta(std::unique_ptr<BitBoard> &board, double alpha, double beta, int depth) const;
 
 
 public:
diff --git a/src/MinimaxSearch.cpp b/src/MinimaxSearch.cpp
index f4cf743..8b1c41c 100644
--- a/src/MinimaxSearch.cpp
+++ b/src/MinimaxSearch.cpp
@@ -32,6 +32,32 @@ double MinimaxSearch::maxValue(bup &board, int currentDepth) const
   return v;
 }
 
+//
+double MinimaxSearch::alphaBeta(bup &board, double alpha, double beta, int depth) const
+{
+  if (depth == maxDepth) return board->utility(board->player());
+
+  // black is max player here
+  double v;
+  if (board->player() == "black") {
+    v = std::numeric_limits<double>::lowest();
+    for (Move move : board->actions()) {
+      bup result = board->result(move);
+      v = std::max(v, alphaBeta(result, alpha, beta, depth + 1));
+      if (v >= beta) return v;
+      alpha = std::max(alpha, v);
+    }
+  } else {
+    v = std::numeric_limits<double>::max();
+    for (Move move : board->actions()) {
+      bup result = board->result(move);
+      v = std::min(v, alphaBeta(result, alpha, beta, depth + 1));
+      if (v <= alpha) return v;
+      beta = std::max(beta, v);
+    }
+  }
+  return v;
+}
 /* Public Functions */
 
 Move MinimaxSearch::minimaxDecision(bup &board) const
@@ -43,10 +69,10 @@ Move MinimaxSearch::minimaxDecision(bup &board) const
     if (bestMove.isEmpty()) {
       bestMove = move;
       bup result = board->result(bestMove);
-      bestMoveValue = minValue(result, 0);
+      bestMoveValue = alphaBeta(result, std::numeric_limits<double>::lowest(), std::numeric_limits<double>::max(), 0);
     } else {
       bup result = board->result(move);
-      double nextMoveValue = minValue(result, 0);
+      double nextMoveValue = alphaBeta(result, std::numeric_limits<double>::lowest(), std::numeric_limits<double>::max(), 0);
       if (bestMoveValue < nextMoveValue) {
         bestMove = move;
         bestMoveValue = nextMoveValue;
@@ -56,3 +82,4 @@ Move MinimaxSearch::minimaxDecision(bup &board) const
 
   return bestMove;
 }
+
diff --git a/src/main.cpp b/src/main.cpp
index 45d8722..fbff2ca 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -10,7 +10,7 @@ int main(int argc, const char * argv[]) {
     std::unique_ptr<BitBoard> board (new BitBoard);
     MinimaxSearch searchDriver;
 
-    for (int i = 0; i < 20; ++i) {
+    for (int i = 0; i < 40; ++i) {
       board->printState();
       Move bestMove = searchDriver.minimaxDecision(board);
       board = board->result(bestMove);