[2024][ruby][18.2]

2024/ruby/day_18.rb

@@ -1,26 +1,24 @@
 falling_bytes = DATA.read.scan(/\d+/).map(&:to_i).each_slice(2).to_a
 
-corrupted = falling_bytes[0,1024]
+MAX = 70
+DELTAS = [[-1,0], [1,0], [0,-1], [0,1]]
 
-max = 70
+def path(corrupted)
+  start = [0,0]
+  stop = [MAX,MAX]
 
-deltas = [[-1,0], [1,0], [0,-1], [0,1]]
+  scores = Hash.new(Float::INFINITY)
-
+  scores[start] = 0
-start = [0,0]
+  frontier = [start]
-stop = [max,max]
+  visited = Set.new
-
+  until scores.has_key?(stop)
-scores = Hash.new(Float::INFINITY)
-scores[start] = 0
-frontier = [start]
-visited = Set.new
-until scores.has_key?(stop)
     current = frontier.shift
     visited << current
 
-  neighbors = deltas.map {|delta|
+    neighbors = DELTAS.map {|delta|
       current.zip(delta).map { _1 + _2 }
     }.select {|xy|
-    xy.all? { (0..max).cover?(_1) }
+      xy.all? { (0..MAX).cover?(_1) }
     }.reject {|xy|
       corrupted.include?(xy) || visited.include?(xy)
     }
@@ -32,9 +30,19 @@ until scores.has_key?(stop)
 
     frontier.uniq!
     frontier.sort_by! { scores.fetch(_1) }
+  end
+
+  scores.fetch(stop)
 end
 
-pp scores.fetch(stop)
+i = (0...falling_bytes.length).bsearch {|i|
+  begin
+    path(falling_bytes[0,i]) && false
+  rescue
+    true
+  end
+}
+puts falling_bytes.fetch(i-1).join(?,)
 
 __END__
 54,47