day 19 more optimizations

day19/sol.py

@@ -56,15 +56,36 @@ def simulate(blueprint, minutes=24):
         buckets[minutes].sort(reverse=True)
         #print(minutes, buckets[minutes][:1])
         for _, robots, resources in buckets[minutes][:limit]:
-            if robots[3]:
+            if 1:
                 geodes = robots[3]*minutes + resources[3]
                 if geodes > max_geodes:
                     max_geodes = geodes
+                elif geodes < max_geodes:
+                    # if the number of geodes we could get if we stopped building robots
+                    # is less than the max such number we've seen so far,
+                    # then prune this node.
+                    #
+                    # this seems like it would be too greedy a rule, but
+                    # somehow it actually works. (i think this is equivalant to
+                    # the rule "always build a geode robot as soon as you can"
+                    # and its validity depends on the input data. (in fact it
+                    # *doesn't* work for the first sample blueprint for part 2.
+                    # but it works on my input so w/e)
+                    #
+                    # decreases the search space enormously
+                    continue
             for robot, cost in items:
                 i = robot_number[robot]
                 if robots[i] >= rmax[i]:
                     # don't build more of 1 robot than we can spend in 1 minute
                     continue
+                if robot != 'geode' and robots[i]*minutes + resources[i] >= minutes*rmax[i]:
+                    # insight from reddit: if we have enough resources on hand and enough
+                    # mining capacity to build any robot that needs it every turn until
+                    # time is up, then we don't need to build any more of that kind of robot
+                    #
+                    # this provides a minor speed-up over just doing the simpler check
+                    continue
 
                 # figure out how soon we can afford it
                 wait = 0
@@ -117,6 +138,6 @@ def solve2(input):
     return t
 
 assert solve(sample) == 33
-#solve(input)
+solve(input)
 solve2(input)