From 7ec040a08b1d474983c0f50a154ca60c40fbd313 Mon Sep 17 00:00:00 2001
From: Petr Baudis <pasky@ucw.cz>
Date: Sat, 8 Mar 2008 12:23:59 +0100
Subject: [PATCH] UCT: Play pass only when we are ready to score

---
 uct/tree.c | 16 +++++++++++++---
 uct/tree.h |  2 +-
 uct/uct.c  |  5 +++--
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/uct/tree.c b/uct/tree.c
index 59a40f8..7097987 100644
--- a/uct/tree.c
+++ b/uct/tree.c
@@ -142,14 +142,24 @@ tree_leaf_node(struct tree_node *node)
 }
 
 struct tree_node *
-tree_best_child(struct tree_node *node)
+tree_best_child(struct tree_node *node, struct board *b, enum stone color)
 {
-	struct tree_node *nbest = node->children;
+	struct tree_node *nbest = NULL;
 	for (struct tree_node *ni = node->children; ni; ni = ni->sibling)
 		// we compare playouts and choose the best-explored
 		// child; comparing values is more brittle
-		if (ni->playouts > nbest->playouts)
+		if (!nbest || ni->playouts > nbest->playouts) {
+			/* Play pass only if we can afford scoring */
+			if (is_pass(ni->coord)) {
+				float score = board_fast_score(b);
+				if (color == S_BLACK)
+					score = -score;
+				//fprintf(stderr, "%d score %f\n", b->last_move.color, score);
+				if (score <= 0)
+					continue;
+			}
 			nbest = ni;
+		}
 	return nbest;
 }
 
diff --git a/uct/tree.h b/uct/tree.h
index 895622d..8da33f4 100644
--- a/uct/tree.h
+++ b/uct/tree.h
@@ -47,7 +47,7 @@ void tree_expand_node(struct tree *tree, struct tree_node *node, struct board *b
 void tree_delete_node(struct tree_node *node);
 void tree_promote_node(struct tree *tree, struct tree_node *node);
 bool tree_leaf_node(struct tree_node *node);
-struct tree_node *tree_best_child(struct tree_node *node);
+struct tree_node *tree_best_child(struct tree_node *node, struct board *b, enum stone color);
 
 struct tree_node *tree_uct_descend(struct tree *tree, struct tree_node *node, int parity, bool allow_pass);
 void tree_uct_update(struct tree_node *node, int result);
diff --git a/uct/uct.c b/uct/uct.c
index 7ef5591..d227aeb 100644
--- a/uct/uct.c
+++ b/uct/uct.c
@@ -114,6 +114,7 @@ uct_genmove(struct engine *e, struct board *b, enum stone color)
 	if (!u->t) {
 tree_init:
 		u->t = tree_init(b);
+		//board_print(b, stderr);
 		u->t->explore_p = u->explore_p;
 	} else {
 		/* XXX: We hope that the opponent didn't suddenly play
@@ -138,7 +139,7 @@ promoted:;
 		}
 
 		if (i > 0 && !(i % 1000)) {
-			struct tree_node *best = tree_best_child(u->t->root);
+			struct tree_node *best = tree_best_child(u->t->root, b, color);
 			if (best && best->playouts >= 500
 			    && ((is_pass(best->coord) && best->value == 1.0)
 			        || best->value >= u->loss_threshold))
@@ -149,7 +150,7 @@ promoted:;
 	if (UDEBUGL(2))
 		tree_dump(u->t);
 
-	struct tree_node *best = tree_best_child(u->t->root);
+	struct tree_node *best = tree_best_child(u->t->root, b, color);
 	if (!best) {
 		tree_done(u->t); u->t = NULL;
 		return coord_copy(pass);
-- 
2.11.4.GIT