From afd49ca1c68d7658e0e7ee4c5f05950fbc9a33f4 Mon Sep 17 00:00:00 2001
From: Alpha Chen <alpha@kejadlen.dev>
Date: Mon, 9 Dec 2024 21:35:44 -0800
Subject: [PATCH] [2024][ruby][10.2]

---
 2024/ruby/day_10.rb | 89 +++++++++++++--------------------------------
 1 file changed, 26 insertions(+), 63 deletions(-)

diff --git a/2024/ruby/day_10.rb b/2024/ruby/day_10.rb
index daca967..41fa51a 100644
--- a/2024/ruby/day_10.rb
+++ b/2024/ruby/day_10.rb
@@ -5,75 +5,38 @@ map = DATA.readlines(chomp: true).flat_map.with_index {|row, y|
 }.to_h
 
 trailheads = map.filter_map { _2 == 0 && _1}
-# trailends = map.select { _2 == 9 }
 
 DELTAS = [[-1, 0], [1, 0], [0, -1], [0, 1]]
 
-def trailends(map, head)
-  queue = [head]
-  visited = Set.new
-  until queue.empty?
-    current = queue.shift
-    visited << current
+def trails(map, head)
+  active = [[head]]
+  finished = []
+  until active.empty?
+    current = active.shift
 
-    queue.concat(
-      DELTAS
-        .map {|d| current.zip(d).map { _1 + _2 } }
-        .select { map.fetch(_1, nil) == map.fetch(current) + 1 }
-        .reject { visited.include?(_1) }
-    )
+    steps = DELTAS
+      .map {|d| current.last.zip(d).map { _1 + _2 } }
+      .select { map.fetch(_1, nil) == map.fetch(current.last) + 1 }
+
+    if steps.empty?
+      finished << current
+    else
+      active.concat(steps.map { current + [_1] })
+    end
   end
-  visited.select { map.fetch(_1) == 9 }
+
+  finished
+    .select { _1.length > 2 && map.fetch(_1.last) == 9 }
+    .uniq
 end
 
-pp trailheads.sum { trailends(map, _1).length }
+pp trailheads.sum { trails(map, _1).length }
 
 __END__
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