diff --git a/2024/ruby/day_10.rb b/2024/ruby/day_10.rb
new file mode 100644
index 0000000..daca967
--- /dev/null
+++ b/2024/ruby/day_10.rb
@@ -0,0 +1,79 @@
+map = DATA.readlines(chomp: true).flat_map.with_index {|row, y|
+  row.chars.map.with_index {|height, x|
+    [[y,x], height == ?. ? nil : height.to_i]
+  }
+}.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
+
+    queue.concat(
+      DELTAS
+        .map {|d| current.zip(d).map { _1 + _2 } }
+        .select { map.fetch(_1, nil) == map.fetch(current) + 1 }
+        .reject { visited.include?(_1) }
+    )
+  end
+  visited.select { map.fetch(_1) == 9 }
+end
+
+pp trailheads.sum { trailends(map, _1).length }
+
+__END__
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