# HG changeset patch
# User Oleksandr Gavenko <gavenkoa@gmail.com>
# Date 1411559482 -10800
# Node ID 4a2551dd179d6156664e489e3df908afd421939f
# Parent  fc6019d22a382deb839b21cf95336cc453bc01b9
Fix: expectimax select best move which lead to less danger among all worst.

diff -r fc6019d22a38 -r 4a2551dd179d ai.js
--- a/ai.js	Wed Sep 24 02:56:41 2014 +0300
+++ b/ai.js	Wed Sep 24 14:51:22 2014 +0300
@@ -380,45 +380,33 @@
     } else {
         this.cache[depth] = [];
     }
-    var weight = 0;
-    var free = 0;
+    var wMin = +Infinity;
     for (var i = 0; i < 3; i++) {
         for (var j = 0; j < 3; j++) {
             if (brd.get(i, j) === 0) {
                 var randBoard = brd.copy();
                 randBoard.set(i, j, 1);
                 var nextBrd = new this.brdEngine();
-                var n = 0, w = 0;
+                var wMax2 = 0;
                 for (var diri = 0; diri < ai.dirs.length; diri++) {
-                    if (randBoard[ai.dirs[diri]](nextBrd)) {
-                        w += this.evalFn(nextBrd, depth+1);
-                        n++;
-                    }
+                    if (randBoard[ai.dirs[diri]](nextBrd))
+                        wMax2 = Math.max(wMax2, this.evalFn(nextBrd, depth+1));
                 }
-                if (n > 0)
-                    w = w / n;
-                weight += this.cfg.balance * w;
+                var wMax4 = 0;
                 if (this.cfg.balance < 1) {
                     randBoard.set(i, j, 2);
-                    var n = 0, w = 0;
                     for (var diri = 0; diri < ai.dirs.length; diri++) {
-                        if (randBoard[ai.dirs[diri]](nextBrd)) {
-                            w += this.evalFn(nextBrd, depth+1);
-                            n++;
-                        }
+                        if (randBoard[ai.dirs[diri]](nextBrd))
+                            wMax4 = Math.max(wMax4, this.evalFn(nextBrd, depth+1));
                     }
-                    if (n > 0)
-                        w = w / n;
-                    weight += this.cfg.balance * w;
+                    var balance = this.cfg.balance;
                 }
-                free++;
+                wMin = Math.min(wMin, balance * wMax2 + (1 - balance) * wMax4);
             }
         }
     }
-    if (free > 0)
-        weight = weight / free;
-    this.cache[depth].push({brd: brd, weight: weight});
-    return weight;
+    this.cache[depth].push({brd: brd, weight: wMin});
+    return wMin;
 }
 /* Mark that next board will be unrelated to previous, so any stored precompution can be cleared. */
 ai.expectimax.prototype.cleanup = function() {