From c40027f12ed3e8a817688ebfbdb83e4f53ac6b60 Mon Sep 17 00:00:00 2001
From: Dece <shgck@pistache.land>
Date: Thu, 19 Dec 2019 00:21:45 +0100
Subject: [PATCH] Day 18

---
 2019/day18.py | 84 +++++++++++++++++++++++++++++----------------------
 2019/grid.py  |  1 +
 2 files changed, 49 insertions(+), 36 deletions(-)

diff --git a/2019/day18.py b/2019/day18.py
index 32a2833..f59572a 100644
--- a/2019/day18.py
+++ b/2019/day18.py
@@ -1,4 +1,5 @@
 import string
+import sys
 
 from grid import Grid
 from vector import v2a
@@ -9,9 +10,6 @@ EX1 = [
     "#b.A.@.a#",
     "#########",
 ]
-# reqs: 
-# a: []
-# b: [a]
 EX2 = [
     "########################",
     "#f.D.E.e.C.b.A.@.a.B.c.#",
@@ -19,41 +17,48 @@ EX2 = [
     "#d.....................#",
     "########################",
 ]
-# reqs: 
-# a: []
-# b: [a]
-# c: [b]
-# d: [b]
-# e: [a, c]
-# f: [a, c, e, d]
-# 
-# - get a
-# - get b
-# - get c or d?
-#   - get c
-#     - get d or e?
-#   - d
 
 
 def main():
     with open("day18.txt", "rt") as input_file:
         lines = input_file.readlines()
     
-    lab = Lab(lines=EX1)
+    lab = Lab(lines=lines)
     lab.dumb_print()
-
     lab.find_positions()
-    pos = lab.start
-    missing_keys = list(lab.key_pos.keys())
-    obtained_keys = set("a")
-    while missing_keys:
+    states = [(lab.start, frozenset(), 0)]
+    state_cache = Grid(value_factory=dict)
+    num_keys = len(lab.key_pos)
+    min_steps = 2**32
+    num_processed = 0
+    while states:
+        num_processed += 1
+        pos, obtained, total_steps = states.pop(0)
+        if len(obtained) == num_keys:
+            print(f"All keys obtained in {total_steps}.")
+            min_steps = min(min_steps, total_steps)
+            continue
 
-        for key, bt in lab.get_all_backtracks(pos).items():
-            steps, reqs, founds = bt
-            if len(reqs - obtained_keys) == 0:
-                print(key, "is accessible")
-        break
+        for key_name, bt in lab.get_missing_backtracks(pos, keys=obtained).items():
+            steps, required, found = bt
+            if len(required - obtained) > 0:
+                continue
+            
+            next_pos = lab.key_pos[key_name]
+            next_obtained = obtained | found | {key_name}
+            next_steps = total_steps + steps
 
+            old_bests = state_cache.getv(next_pos[0], next_pos[1])
+            if next_obtained not in old_bests or old_bests[next_obtained] > next_steps:
+                print("o", end="")
+                states.append((next_pos, next_obtained, next_steps))
+                old_bests[next_obtained] = next_steps
+            print(".", end="")
+
+        if num_processed % 100 == 0:
+            print(f"[{num_processed}/{len(states)}]", end="")
+        sys.stdout.flush()
+    print(f"Minimal number of steps to get all keys: {min_steps}.")
 
 class Lab(Grid):
 
@@ -77,13 +82,18 @@ class Lab(Grid):
                 self.door_pos[v] = (x, y)
         self.setv(self.start[0], self.start[1], Lab.TILE_PATH)
     
-    def get_all_backtracks(self, start):
-        return {
-            kname: self.backtrack(self.path(start, kpos), kpos, start)
-            for kname, kpos in self.key_pos.items()
-        }
+    def get_missing_backtracks(self, start, keys=set()):
+        backtracks = {}
+        for kname, kpos in self.key_pos.items():
+            if kname in keys:
+                continue
+            path = self.path(start, kpos, keys=keys)
+            if path is None:
+                continue
+            backtracks[kname] = self.backtrack(path, kpos, start)
+        return backtracks
 
-    def path(self, s, e):
+    def path(self, s, e, keys=set()):
         discovered = Grid(value_factory=bool)
         discovered.setv(s[0], s[1], True)
         parents = {}
@@ -96,12 +106,14 @@ class Lab(Grid):
             for near_pos, near_tile in nears.items():
                 if near_tile == Lab.TILE_WALL:
                     continue
+                if near_tile in string.ascii_uppercase and near_tile.lower() not in keys:
+                    continue
                 if discovered.getv(near_pos[0], near_pos[1]):
                     continue
                 discovered.setv(near_pos[0], near_pos[1], True)
                 parents[near_pos] = pos
                 q.append(near_pos)
-        return parents
+        return None
 
     def backtrack(self, parents, pos, end):
         count = 0
@@ -115,7 +127,7 @@ class Lab(Grid):
                 requirements.add(tile.lower())
             elif tile in string.ascii_lowercase:
                 keys_found.add(tile)
-        return count, requirements, keys_found
+        return count, requirements, frozenset(keys_found)
 
 
 if __name__ == "__main__":
diff --git a/2019/grid.py b/2019/grid.py
index f442284..2365fca 100644
--- a/2019/grid.py
+++ b/2019/grid.py
@@ -37,6 +37,7 @@ class Grid:
             print()
 
     def print_near(self, p, view_size=2):
+        """Print near values in an area of view_size. Works iff keys support addition."""
         for dy in range(-view_size, view_size + 1):
             print("".join([
                 self.g[p[1] + dy][p[0] + dx]