Fixed alphabeta_search

games.py

@@ -68,7 +68,17 @@ def min_value(state, alpha, beta):
         return v
 
     # Body of alphabeta_search:
-    return max_value(state, -infinity, infinity)
+    v = -infinity
+    best_action = None
+    for a in game.actions(state):
+        val = min_value(game.result(state, a), alpha, beta)
+        if val > v:
+            v = val
+            best_action = a
+        if v >= beta:
+            break
+        alpha = max(alpha, v)
+    return best_action
 
 
 def alphabeta_search(state, game, d=4, cutoff_test=None, eval_fn=None):
@@ -107,7 +117,17 @@ def min_value(state, alpha, beta, depth):
     cutoff_test = (cutoff_test or
                    (lambda state, depth: depth > d or game.terminal_test(state)))
     eval_fn = eval_fn or (lambda state: game.utility(state, player))
-    return max_value(state, -infinity, infinity, 0)
+    v = -infinity
+    best_action = None
+    for a in game.actions(state):
+        val = min_value(game.result(state, a), alpha, beta, 1)
+        if val > v:
+            v = val
+            best_action = a
+        if v >= beta:
+            break
+        alpha = max(alpha, v)
+    return best_action
 
 #______________________________________________________________________________
 # Players for Games